No.1 seed Ashleigh Barty triumphed in 2021's second clash of reigning Grand Slam champions, defeating No.9 seed Barbora Krejcikova 6-2, 6-4 in one hour and 11 minutes to reach her second straight Western & Southern Open semifinal.

Barty will meet the unseeded and resurgent Angelique Kerber in a reprise of the Wimbledon semifinals. The German moved through after No.11 seed Petra Kvitova was forced to retire trailing 6-3, 3-3.

Wimbledon champion Barty extended her season record to 38-7 with her victory, in which she recovered from 2-4 down in the second set. It is Barty's second win in as many meetings with Roland Garros champion Krejcikova, having also defeated the Czech 7-5, 6-3 in the fourth round of Wimbledon. Both those pro encounters have taken place a decade after the pair first met in 2011 Junior Fed Cup action, with Barty winning that match 6-3, 6-1.

Barty also made the last four in Cincinnati in 2019 with victories over Maria Sharapova and Maria Sakkari before being stopped by Svetlana Kuznetsova. She missed the 2020 edition of the tournament due to the Covid-19 pandemic.

The last 5 matches between reigning Grand Slam champions
2021 Cincinnati QF, Ashleigh Barty d. Barbora Krejcikova 6-2, 6-4
2021 Australian Open R4, Simona Halep d. Iga Swiatek 3-6, 6-1, 6-4
2019 Shenzhen WTA Finals RR, Simona Halep d. Bianca Andreescu 3-6, 7-6(6), 6-3
2019 Beijing F, Naomi Osaka d. Ashleigh Barty 3-6, 6-3, 6-2
2019 Beijing QF, Naomi Osaka d. Bianca Andreescu 5-7, 6-3, 6-4

Key to the match: A cagy contest between two of the tour's best tacticians found both players approaching rallies carefully, as though seeking to avoid getting lured into the other's traps. This paid off for Barty, who reaped the rewards of mixing up pace and spin while playing down the middle of the court, giving Krejcikova little to work with.

But for all the nuances, it was the Australian's serve that was the bedrock of her game. Barty's 52% first serve percentage wasn't her finest - though still better than Krejcikova's 47% - but the World No.1 always seemed to have a clutch big serve up her sleeve, raining down seven aces in total.

Turning point: Improved serving and greater aggression saw Krejcikova swing momentum her way at the start of the second set, and the World No.10 stood two games from forcing a decider at 4-2. But with her back to the wall, Barty raised the stakes.

Three of Barty's finest winners, including two scintillating passes, signalled that she had found a new level and opened the door for the break back. Krejcikova's forehand, which has been in-and-out all day, fell away as her unforced error tally rose to 25. Even her famed net skills couldn't save her: the final two points of the match were volley errors from Krejcikova, the last forced by Barty's low, biting slice return.

Quotable: "I travel with a French press and an AeroPress, just to have two options. Usually every tournament we go to, one of us has a café that we have been to before, so I have got a little section of all my local cafés from the tournaments, so we try and get out to those if we can. This year, some places we haven't been able to; some places we have. It's been nice to get some sort of a mixture, but I'm pretty simple. I'm just a black coffee cup in the morning, and then I'm set."
-Ashleigh Barty on the importance of coffee in the morning.

Kerber progresses past ailing Kvitova

The 16th installment of Kerber and Kvitova's 14-year rivalry ended in unfortunate fashion with the first retirement of the series.

A serve-dominated first set that featured few rallies was edged by Kerber, after Kvitova coughed up two double faults and two forehand errors at 4-4 for the sole break. The Czech, who had revealed that she was "fighting with a health issue" following her third-round win over Ons Jabeur, began to visibly struggle as the second set got underway.

Kvitova managed to take a 3-0 lead in the second set by dint of all-out first-strike shotmaking, despite needing to take an emergency bathroom break after the second game. But Kerber adjusted to playing an ailing opponent and clawed her way back to 3-3 before Kvitova called it quits, retiring due to gastrointestinal illness. 

Kerber, who defeated Kvitova in a third-set tiebreak in June's Bad Homburg semifinals, levels their overall head-to-head at eight wins apiece with the result. The World No.22 moves into her third straight semifinal, and third in Cincinnati following final runs in 2012 and 2016.

Wimbledon reprise set in Cincinnati

One month ago, Barty and Kerber squared off for a stellar showdown in the Wimbledon semifinals, which Barty won 6-3, 7-6(3) en route to her second Grand Slam crown. That result put the World No.1 ahead 3-2 in their head-to-head series. Previously, Kerber had won two encounters on Australian hard courts (in the 2017 Brisbane second round and 2018 Sydney final), while Barty had taken their two meetings on Chinese hard courts (in the 2017 Zhuhai round robin and 2018 Wuhan third round).

Kerber turned her season around during the grass swing in June: her record going into it had been 9-10, but she has been 14-1 since the start of Bad Homburg. To Barty, though, she's always been a formidable opponent. 

"She's really locked down into the Angie of old."

- - Ashleigh Barty on Angelique Kerber's recent renaissance.

"Angie, she's never been far off her best," said Barty. "She never is. Even on some days where she's not having or playing her best tennis, she finds a way to scrap and fight and stay in matches and give herself an opportunity. She's one of the best competitors in the world. She knows how to play big tournaments, knows how to play big matches.

"She's really locked down into the Angie of old, I think, in a sense where she's confident, she's aggressive, but she's able to run and to move and put the ball in tricky spots, to not let you dictate too much. That's a challenge of when you play against Angie - you have to ride a fine line of not pressing too much, but not being too defensive where she can move you around the court. "