Carlos Alcaraz suffered a shock defeat at the Cincinnati Open as Gael Monfils came from a set down to prevail from a rain-delayed encounter.

Monfils was 3-1 up in a second-set tie-break before rain stopped play on Thursday, but returned 24 hours later to win 4-6 7-6 (7-5) 6-4.

Once play resumed on Friday, Monfils continued where he left off but squandered three set points before eventually taking the tie this distance. 

Last year's runner-up Alcaraz struggled in the opening exchanges, with his French opponent finding a decisive break in the third game as Monfils took control of proceedings in Ohio. 

And Monfils' experience ultimately told, as the 37-year-old held out for the remainder of his service games to set up a meeting with Holger Rune in the last 16, condemning Alcaraz to a shock exit.

World number one Jannik Sinner, meanwhile, had no need to take to the court on his 23rd birthday, as he was handed a walkover following Jordan Thompson's withdrawal.

Data Debrief: The old head prevails

Monfils is the oldest player to defeat an opponent ranked in the ATP top-three since Jimmy Connors defeated Michael Stich in Memphis in 1992.

The world number 46 starred on serve, firing 15 aces throughout the contest compared to Alcaraz's seven, while also clawing back six of the seven break points he faced.

World number one Carlos Alcaraz defeated Tommy Paul in a three-set thriller to reach the quarter-finals of the Western and Southern Open in Cincinnati.

Wimbledon champion Alcaraz outlasted the American 7-6 (6) 6-7(0) 6-3 in a gruelling contest that lasted more than three hours.

The Spaniard suffered a three-set defeat against the American in the quarter-finals at the Toronto Masters last week.

Paul got the first break to lead 4-2, before Alcaraz rallied to bring up the tie-break, which he eventually claimed 8-6.

The second set proved another tight affair, with both players losing three service games at 5-5.

Paul saved three match points in a marathon 12th game which lasted more than 15 minutes to go into another tie-break.

This time, though, the American took control after an early mini-break to race into a 3-0 lead before then sweeping it to love.

Alcaraz broke in the first game of the deciding set, which he was leading 4-3 when rain forced play to be suspended after three hours and two minutes of a pulsating contest.

Following a delay of around an hour, the players headed out on court – but the match was soon paused again as the drizzle returned along with strong winds before the pair went off back inside.

When they were finally able to return to the court, Alcaraz picked up where he left off, clinching the next two games and sealing a trip to the quarter-finals.

Earlier on Thursday, Alexander Zverev battled past world number three Daniil Medvedev 6-4 5-7 6-4 to end a four-match losing streak against the Russian.

Stefanos Tsitsipas, the fourth seed, is out after he was beaten 6-3 6-4 by Poland’s Hubert Hurkacz, who recorded a first win over a top-10 ranked player in six matches.

Hurkacz goes on to play lucky loser Alexei Popyrin after the Australian earlier defeated Emil Ruusuvuori 6-2 1-6 6-3 to reach his first ATP Masters 1000 quarter-final.

Zverev will face Adrian Mannarino in the last eight. The Frenchman progressed after American wildcard Mackenzie McDonald retired during the second set of their third-round match, with Mannarino ahead 6-4 3-0.

The run of veteran Swiss Stan Wawrinka – who had been given a wildcard entry and knocked out 10th seed Frances Tiafoe in the last round – was ended with a 6-4 6-2 defeat by qualifier Max Purcell.

The Australian, who upset world number seven Casper Ruud on Wednesday, will next face Alcaraz.

Petra Kvitova fended off home favourite Madison Keys to reach the Western and Southern Open final and secure a return to the world's top 20.

The two-time Wimbledon champion battled to a 6-7 (6-8) 6-4 6-3 victory in two hours and 18 minutes, saying the match had been "mentally so tough".

Both players had taken significant scalps to reach this stage, with Keys knocking out world number one Iga Swiatek and Kvitova ousting Wimbledon runner-up Ons Jabeur.

Kvitova reached semi-finals at Cincinnati in 2012 and 2018 and lost three-set battles on both occasions, but this time she came good in the decider to earn a first final appearance at the event and a 40th overall in her WTA career.

The 32-year-old Czech slipped an early break adrift in the opening set before fighting back to force a tie-break. She came from behind in that, too, to level up at 6-6, only for hard-hitting American Keys to win the next two points, the first with a sizzling backhand winner.

Kvitova sensed she was still firmly in the match, however, and surges to 3-1 in each of the next two sets provided the platform to fully turn around the contest.

A 12th WTA 1000-level final awaits her, and she will go to 20th in the rankings should she lose Sunday's final and up to 15th if she carries off the title.

Kvitova said of her win: "It was incredibly tough. I expected it would be tough, but I didn't expect it that tough. Madison played unbelievable.

"She played an amazing tie-break, but I tried to keep going, be there and be a little calmer than before and wait for the chances. It was an incredible match, and I'm really happy that I made it somehow.

"I don't really care about the ranking. Being in the final, that's more important, and that's why I'm playing tennis: to be in finals and fighting for a trophy."

She awaited the winner of the second semi-final between Aryna Sabalenka and Caroline Garcia.

Madison Keys stunned top seed Iga Swiatek 6-3 6-4 to book her place in the quarter-finals of the Western & Southern Open on Thursday.

Keys arrived in the contest seeking a first career victory over a reigning world number one in six attempts, having failed to win a set in each of the previous five.

The 2019 champion had also lost her previous two showdowns with Swiatek, including a resounding 6-1 6-0 defeat in the Indian Wells Open quarter-finals earlier this year.

After the first games went with serve, Keys went into overdrive; reeling off nine successive games to take full command of the contest at 6-3 5-0.

Swiatek rallied as she rescued match point to avoid the bagel, winning 11 of 12 points to reduce the second-set deficit to 5-3.

The winner of six WTA titles this season, the Pole saved a further match point in the ninth game before claiming what appeared to be another crucial break of serve.

However, former US Open finalist Keys responded magnificently to make it third time lucky against Swiatek, who is now 4-4 since her 37-match winning streak ended with defeat by Alize Cornet at Wimbledon.

Emma Raducanu admitted she has been "too tense" in recent defeats and is aiming to play more freely as she prepares to defend her US Open title.

Raducanu has struggled to follow up last year's shock win at Flushing Meadow, but she appears to have hit form at just the right time.

The 19-year-old has beaten both Serena Williams and Victoria Azarenka in straight sets during this week's Western and Southern Open in Cincinnati, dropping just four games against Williams and two against Azarenka.

Her win against Azarenka on Wednesday was just Raducanu's third career victory against a top-25 opponent, after beating Belinda Bencic and Maria Sakkari on her way to winning last year's US Open.

Speaking after her win against the Belarusian, Raducanu said: "I think I have tried a lot of things, and this year I think some matches, I have lost a lot of matches from leading situations and probably just played too tense.

"I think that I just need to swing, and I just said that these two tournaments, or this tournament especially, I'm just going to swing freely and take that and see what happens."

Raducanu also said she will wait until after the tournament to reflect on beating two multiple grand slam champions with relative ease.

"I think after the tournament I actually have to take a step back and be like, 'Look, you just beat two unbelievable champions'," she said. "It's a pretty good achievement. You know how difficult the wins are to come by."

The number 10 seed will face seventh seed Jessica Pegula in the third round in Cincinnati on Thursday.