Former Wimbledon champ Kvitova into Eastbourne quarter-finals
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Kvitova, who won Wimbledon in 2011 and 2014, is using the WTA Tour event on England's south coast to prepare for the grass-court Grand Slam, which starts on Monday.
The 32-year-old was in danger of a shock defeat against Boulter after the world number 127 took the first set of their last-16 clash in warm temperatures at Devonshire Park.
Boulter had knocked out last year's Wimbledon runner-up Karolina Pliskova in the previous round.
But former world number two Kvitova showed her class as she took the second set at a canter.
The Czech, who last reached a Grand Slam final in Australia in 2019, held her nerve in a tense decider to win in two hours and 23 minutes.
In the Eastbourne men's singles, Cameron Norrie defeated Brandon Nakashima 6-4, 6-2 for his first win on grass this season.
The British number one, who will be seeded ninth at Wimbledon, suffered a shock first-round exit at Queen's Club last week.
But Norrie bounced back at Eastbourne with an accomplished display against Nakashima, breaking the American's serve three times.
"It would have been nice to go deeper at Queen's but now looking to get some more matches and time on the grass before Wimbledon here," Norrie said.