Two Wimbledon champions booked spots in the Round of 16 of the Agel Open as Elena Rybakina and Petra Kvitova each gritted through big-hitting three-set tussles on Monday.

Reigning Wimbledon champion Rybakina of Kazahkstan fought past Madison Keys of the United States 5-7, 6-3, 6-3 in two hours and 14 minutes, ending a two-match losing streak.

A quarterfinalist in Ostrava last year, Rybakina won 60 percent of points returning the Keys second service on her way to the come-from-behind victory. Rybakina slammed seven aces in the affair as well.

Keys had beaten Rybakina in their first two meetings, both coming this season at Roland Garros and Cincinnati. The American was a set away from a third successive victory over Rybakina as she led by a set and a break at 7-5, 1-0.

However, Rybakina earned her first break of the day in the very next game, and she kept her momentum going by breaking Keys again for a 3-1 lead. Rybakina held on to take the second set, with five fewer unforced errors than she had in the opening frame.

More from Ostrava Day 1: Alexandrova gains first win over Azarenka in Ostrava

The third set featured sterling passing winners by both players in the early going, but Rybakina took command for good with her second break of the set for 3-2.

At 5-3, Keys fended off three match points with powerful groundstrokes, but Rybakina converted her fourth chance by following a big return up with a forehand winner that fell just inside the baseline.

After Rybakina triumphed on Center Court, Czech Kvitova followed with a tight 6-3, 2-6, 6-4 win over another American, qualifier Bernarda Pera. Kvitova had 35 winners to just 21 unforced errors in the clash.

Kvitova, currently ranked World No.20, took just over two hours to prevail in her first meeting with 45th-ranked Pera, who has risen up the rankings in 2022 after winning her first two WTA titles in Budapest and Hamburg.

Read more: Top seed Swiatek rested and feeling at home in Ostrava

Kvitova, a former World No.2 who won Wimbledon in 2011 and 2014, got off to a hot start on home soil, racing to a 5-0 lead. Pera, though, started to pull her way back into the match at the tail end of the opener, and the American eased through the second set.

Pera powered her way to an early break in the third set, leading 2-0, but sturdy returns by both players meant five of the first seven games of the set went against serve. The flurry of aggressive return games left Kvitova standing ahead by a break at 4-3.

Pera fired her first ace of the match to hold for 5-4, putting pressure on Kvitova to serve out the match. Homeland hope Kvitova was up to the task, firing her 10th ace to set up double match point, and her 11th ace to seal the win.

Kvitova will meet another big hitter, No.2 seed Paula Badosa of Spain, in her next match. World No.4 Badosa, as one of the top four seeded players, received a bye into the Round of 16. The head-to-head between Kvitova and Badosa is deadlocked at 1-1.