World number nine Auger-Aliassime needed just an hour and 24 minutes to see off home hope Elliot Benchetrit 6-3 6-3.
He saved all six break points he faced to set up a second-round meeting with Slovak lefty Alex Molcan in Morocco.
But Evans' stay in Marrakech is over after he succumbed to a surprise 6-4 6-2 loss to Pablo Andujar. The Briton has now won just one of his last five matches on tour.
Lorenzo Musetti has endured a tough start to 2022 and headed into this tournament 5-7 on the year.
However, the 20-year-old delivered a reminder of his potential with a straight-sets win over fourth seed Albert Ramos-Vinolas.
Joao Sousa knocked out fifth seed Federico Delbonis but sixth seed Botic van de Zandschulp and eighth seed Laslo Djere did prevail, as did veteran Richard Gasquet.
Gaston rallied after dropping serve twice in the opening set, prevailing 3-6 6-4 7-5 to become the first player to book their spot in the last-16.
Jaume Munar followed suit with a 6-4 6-4 victory over Elliot Benchetrit.
Elsewhere, at the Estoril Open, victories for Pedro Cachin and Sebastian Baez set up a potential hat-trick of wins for Argentine players.
Cachin beat Tseng Chun-hsin 6-4 6-4 and Baez overcame Radu Albot 7-5 7-6 (7-3) but seventh seed Diego Schwartzman could not follow up with a win of his own, losing 6-3 7-6 (10-8) to Marco Cecchinato.
Fabio Fognini also booked his spot in the last 16 by beating compatriot Alessandro Giannessi in straight sets.
Experienced Belgian Goffin is a five-time tournament winner on the ATP Tour, and his Slovakian opponent is chasing his first title at this level.
However, their one past meeting went Molcan's way when they met in the Melbourne ATP 250 tournament in January, and although that match was on hardcourts and this final is on clay, Goffin respects his left-handed opponent's game.
Goffin made sure of his place in the title match with a 6-3 6-3 win over Argentinian Federico Coria, while Molcan, who beat Felix Auger-Aliassime earlier in the week, was a 6-1 7-5 victor against Serbian Laslo Djere.
Speaking of the threat posed by Molcan, Goffin said: "He's a great fighter, he's moving so well. He's lefty, so he's using his lefty game really well on clay, especially two days ago against Felix, he played well. So it's a tough opponent."
Goffin, quoted on the ATP Tour website, said he was pleased to get his clay season under way in fine style, even if he felt jittery at times against Coria.
"I managed to deal with my emotions at the end to finish the match, so I'm happy to play another final, especially here, the first tournament on clay," Goffin said. "I will give everything tomorrow."
Slovakian Molcan, in search of a first triumph at main tour level, came flying out of the blocks, but ultimately Belgian Goffin's experience showed as he recorded a 3-6 6-3 6-3 victory.
World number 65 Molcan, who defeated Goffin in the first week of the season in Melbourne, was in early control of this meeting in Marrakesh, a set to the good and serving at 2-1 up in the second.
However, former world number seven Goffin responded from that point onwards and did not look back as he won in one hour and 58 minutes.
Goffin feels he can take confidence from this success into the rest of the clay-court segment of the 2022 season.
"I'm very happy, proud of my week. It was not easy, a lot of tough matches," Goffin said. "But at the end, I have my sixth title, here in Marrakesh. It gives me a lot of happiness and confidence for the season on the clay.
"It was the case twice before that match that I lost the first set and I always stayed calm the whole week to turn it around. It was the case again today, because he was playing well.
"He was better than me in the first set, and then I managed to play better and better, serving better, being more aggressive in the middle of the second. I was the better player [after that]."
Quoted on the ATP website, Goffin said: "I was playing even better in the third set, so I'm really happy the way I finished with another break [and] a good match point. I didn't want to serve for the match, I preferred to finish with a break."
Molcan reflected on a positive week in Morocco that saw him most notably beat top seed Felix Auger-Aliassime.
"It was an amazing week for me," he said. "I won a lot of matches and enjoyed it very much."
The former world number seven saw off the Spaniard in a three-set quarter-final to book his place in the last four, 14 months on from his last title in the Open Sud de France.
Goffin, ranked 74th in the world and unseeded for the event in Marrakech, was forced to fight across a gruelling first set, which Baena edged out in a tie-break.
But he fought back to level things in the second before sweeping through the third set unanswered.
Goffin will face Argentine Federico Coria following the latter's 6-7 (1-7) 6-1 6-4 comeback win over Richard Gasquet.
Elsewhere, Alex Molcan's run continued after the Slovakian won 4-6 6-3 6-4 against Botic van de Zandschulp following his last-16 victory over top seed Felix Auger-Aliassime.
He will now face Laslo Djere in the last four after the Serbian overcame Italy's Lorenzo Musetti in straight sets.
The former world number seven is in the hunt for a first title of the season, and defeated Damir Dzumhur 6-2 7-6 (7-3) in his first match on Wednesday.
That victory teed up a last-16 tie with Andujar, who defeated second seed Dan Evans in his first-round match.
The 36-year-old Spaniard is something of a specialist in Marrakech, having won this tournament three times, in 2011, 2012 and 2018.
Young Italian prospect Lorenzo Musetti overcame Andujar's compatriot Carlos Taberner 6-1 6-7 (3-7) 6-3 to become the first player to reach the quarter-finals.
Musetti, who reached the last 16 at last year's French Open and featured at the ATP Next Gen Finals, has had a tough start to 2022, only reaching one other quarter-final so far.
Serbian eighth seed Laslo Djere followed Musetti into the last eight by beating Malek Jaziri 6-4 6-2.
Qualifier Mirza Basic sprung a surprise to overcome Kamil Majchrzak 4-6 6-4 6-1, while Vit Kopriva defeated Bernabe Zapata Miralles in straight sets.
World number 172 Pavel Kotov claimed the scalp of a top-100 player, bouncing back from a first-set bagel to beat Tallon Griekspoor 0-6 6-2 6-2.
Having enjoyed the best season of his career in 2022, Ruud was bidding for his first trophy success of 2023 in Portugal, and the world number five made a flying start to his clash with Kecmanovic.
Ruud wrapped up the opener in just 36 minutes, taking control with a huge forehand winner to break in just the third game.
The Norwegian navigated two three-set contests in order to reach the showpiece, and it looked like another of his matches may go the distance when Kecmanovic recovered to force a second-set tie-break.
However, a dipping backhand saw Ruud secure the second of two crucial mini breaks, and he took the first of his three championship points to cap a fine week with silverware, sealing a 6-2 7-6 (7-3) win.
Elsewhere, Carballes Baena won just his second career title, triumphing on the clay in Marrakesh where he beat Alexandre Muller 4-6 7-6 (7-3) 6-2.
France's Muller showed no signs of being overawed on his first final outing as he took the opener in impressive fashion, but Carballes Baena edged a tie-break in the second before dominating the decider.
Carballes Baena's triumph – recorded in just under three hours – gave him his first title since the 2018 Ecuador Open, which also came on his favoured clay surface.
The number one seed, competing in his first semi-final of the season, prevailed 6-4 3-6 7-6 (7-2) in Portugal to move within one match of a 10th singles title.
Ruud broke his opponent's serve in the opening game and saw out the first set, but Halys – competing in his first ATP Tour semi-final – hit back in the second to prolong the match.
Both men held as the contest went the distance, but Ruud's quality told as he raced 3-0 ahead in the deciding tie-break and did not look back as he set up a final with Kecmanovic.
World number 40 Kecmanovic needed a little over an hour to beat sixth seed Cecchinato, who had surprised Alejandro Davidovich Fokina in the previous round.
Kecmanovic, aiming to add to his only previous singles success in Kitzbuhel three years ago, held serve throughout to claim a 6-3 6-1 win over the 2018 French Open semi-finalist.
Elsewhere on Saturday, the final seeded player fell at the Grand Prix Hassan II as Dan Evans was defeated 2-6 6-4 6-2 by Roberto Carballes Baena.
Carballes Baena has now eliminated three seeded players and will face Alexandre Muller in Sunday's final after the Frenchman saw off Pavel Kotov in straight sets.
Muller edged a first-set tie-break and proved too strong in the second as he saw out a 7-6 (7-3) 7-5 victory in Marrakesh.
The former US Open champion and two-time Roland Garros finalist had gone his previous four ATP Tour-level events without a win.
But Thiem, once ranked as high as third in the world, ended the drought with a 3-6 6-3 6-4 defeat of compatriot Sebastian Ofner.
He will next face American Ben Shelton, who defeated Constant Lestienne 7-5 7-5.
Meanwhile, there were three shocks at the Grand Prix Hassan II in Marrakesh.
Roberto Carballes Baena came from a set down to beat fifth seed Maxime Cressy, Alexandre Muller overcame sixth seed Richard Gasquet, and qualifier Andrea Vavassori defeated eighth seed Nicolas Jarry.
Making his debut in Marrakech, Auger-Aliassime arrived off the back of an impressive start to 2022.
Indeed, the world number nine had already triumphed in Rotterdam and been runner-up to Andrey Rublev in Marseille.
But he came unstuck at the hands of the player ranked 56 places lower, with Molcan securing his first career win over a top-10 player.
The Slovakian crucially broke in game nine on the way to taking the opening set. Auger-Aliassime, who hit 10 double faults during the contest, responded by dominating the second, while the players exchanged breaks in a decider that went to a tie-break.
The top seed forced match point at 7-6 up, but Molcan held on by reeling off the next three to secure a dramatic victory.
David Goffin, meanwhile, claimed his 300th tour-level win as he came from behind to defeat three-time champion Pablo Andujar.
Andujar had seen off second seed Dan Evans in the first round but, despite making a fast start against Goffin, it was the Belgian who triumphed 5-7 7-6 (7-4) 6-3.
Federico Coria overcame Mirza Basic in straight sets, while Roberto Carballes Baena defeated Portugal's Joao Sousa 6-2 7-6 (7-4) and Richard Gasquet saw off Pavel Kotov.
