Andrey Rublev and Andy Murray battled to outlast their opponents at the Qatar Open, while Daniil Medvedev breezed into the quarter-finals.
Top seed Rublev, who won this tournament in 2020, responded to a first-set setback to rally to a 1-6 6-1 7-6 (8-6) win over Tallon Griekspoor on Wednesday.
The world number five was staring at a fourth opening-round defeat in five appearances this year but saved three match points en route to fighting back from 5-2 down in the decider.
Murray and fourth seed Alexander Zverev played out another three-set thriller in the Middle East, with the former world number one triumphing 7-6 (7-5) 2-6 7-5.
That clash lasted three hours and three minutes in another marathon match for Murray after defeating Italian Lorenzo Sonego in a final-set tie-break in the first round.
Medvedev (3) had no such difficulty in a comfortable 6-4 6-3 victory over world number 147 Liam Broady.
Second seed Felix Auger-Aliassime had to regain his composure during his debut in Doha, but ultimately prevailed 4-6 6-1 6-4 against Jason Kubler.
World number eight Auger-Aliassime had lost his only previous meeting with Kubler, and an upset was on the cards after the Canadian was broken in the third game and was unable to recover.
Yet he found his form with a blistering second set, reeling off five straight games to restore parity and keeping his cool in the decider.
That victory teed up a last-eight meeting with seventh seed Alejandro Davidovich Fokina, who downed Kwon Soon-woo 6-3 6-2.
Jiri Lehecka will meet favourite Rublev after beating Emil Ruusuvuori 6-2 7-6 (7-2), while Botic Van De Zandschulp was shocked by world number 170 Alexandre Muller in a straight-sets defeat.
Elsewhere at the Open 13 Provence, fifth seed Maxime Cressy fell to a surprise second-round elimination after a 6-7 (5-7) 6-4 6-3 loss to home favourite Benjamin Bonzi.
There was no such luck for the other Frenchmen in Marseille as Alexander Bublik eased past Gregoire Barrere, while Stan Wawrinka beat Richard Gasquet 4-6 7-5 6-2 to reach the last eight.