No.8 seed Karolina Pliskova booked a return engagement into the round of 16 at Wimbledon after defeating her fellow Czech Tereza Martincova, 6-3, 6-3 on No.2 Court on Friday.

Pliskova, who posted fourth-round showings in the last two editions of the grass-court major, took an hour and 38 minutes to oust her countrywoman, in the only third-round match of the week between compatriots.

"I think [Martincova] was really playing well," Pliskova said in her post-match press conference. "I thought I did well at the important moments. I was holding my serve. Any time it was a close situation, I think I played really good shots. 

"Overall, I think all the matches which I played here, I think I did quite a good job. Super solid, serving well, and playing quite the game I want to play, actually."

Pliskova struggled past Martincova in their only previous meeting, needing two tiebreak sets to notch a win in the first round of the 2019 US Open. This time, the former World No.1 had less difficulty quelling Martincova's challenge, despite a nearly hour-long opening set filled with protracted games.

"I think the score doesn't really look the way it was, because I think there were a couple close games," Pliskova said. "Actually, the first two games just took 20 minutes."

30 winners flew off the racquet of Pliskova, nearly tripling the winner count from Martincova. Pliskova converted four of her 12 chances to break, while Martincova also had a number of opportunities but finished only 1-for-8 on break points.

Despite the loss, Martincova, currently at a career-high ranking of World No.87, has had a breakthrough grass-court season, with quarterfinal runs at Birmingham and Nottingham preceding her first third-round showing at a Grand Slam event this week.

The pair of Czechs gritted through tough holds in the first two games of the affair, with Martincova saving four break points and Pliskova saving three. However, Pliskova got more chances in the next game, and claimed her 2-1 lead after a long miscue by Martincova on break point.

At 4-2, Pliskova notched an insurance break in another long game for good measure, converting her fourth break point to move ahead 5-2. That came in handy after Martincova used solid returning to claw one break back, but Pliskova was undeterred and broke the unseeded player in the very next game to clinch the set after 55 hard-fought minutes.

In the second set, Pliskova fought off four break points en route to a hold for 3-2, which proved to be crucial as she broke Martincova in the subsequent game to take a commanding 4-2 lead. Pliskova eased to victory from there, storming to triple match point at 5-3 and forcing an errant return with a big serve on the third of those chances.

Next up for Pliskova will be a meeting in the round of 16 with the discovery of this year's grass-court season, Liudmila Samsonova of Russia.

Samsonova, who was given a wildcard into the main draw after she stormed to her first WTA singles title as a qualifier in Berlin just two weeks ago, defeated 2017 US Open champion Sloane Stephens of the United States, 6-2, 2-6, 6-4, to clinch a spot in the second week.

The 22-year-old's victory continues a rapid ascent over the last three weeks, as she blasted from outside the Top 100 up to her current ranking of World No.65. She is projected to improve that standing even further after her two-hour win over former World No.3 Stephens.

Samsonova came into the match with a win over Stephens already under her belt, having defeated the American in their only previous meeting, in the first round of Brisbane last season, by a very similar scoreline (6-4, 2-6, 6-3).

With an array of powerful shots at her disposal, Samsonova shook off a second-set comeback by Stephens, slamming 31 winners to just eight by the American. Samsonova's first-strike tennis also yielded 44 unforced errors, but her six breaks of service pushed her over the finish line.

Three of those breaks came in the opening frame as Samsonova's great grass-court form powered her to a one-set lead. However, Stephens charged back to take the second set and level the tilt, drawing errors from the Russian and beginning to match her in firepower.

But Stephens faltered in the opening game of the decider, dropping serve right away after Samsonova forced an error from the American's backhand side on break point.

Stephens had one final chance to break Samsonova and get back level at 4-3, but the Russian saved that with a well-timed winning volley. Samsonova was relatively untroubled the rest of the way, locking up a fourth-round appearance in her Wimbledon main-draw debut.

In the late match of the day, No.23 seed Madison Keys of the United States earned her spot in the fourth round with a 7-5, 6-3 victory over No.13 seed Elise Mertens of Belgium on No.1 Court.

Keys is back into the fourth round of Wimbledon for the first time since 2016. Her best result in London is a quarterfinal showing in 2015, and she is now one win away from matching that feat.

Keys extended her perfect record against Mertens, improving to 3-0 against the Belgian (6-0 in sets). All of their meetings have come at Grand Slam events, with this Wimbledon victory being added to wins at the 2017 US Open (en route to her Grand Slam final) and the 2019 Australian Open.

"I knew points were going to be more difficult," Keys said, in her post-match press conference. "I knew [Mertens] was going to have a lot of great gets. I knew if I could just try to play my game and focus on that and not really get ahead of myself, then good things could happen."

The players powered through two relatively close sets in just an hour and 15 minutes, routinely rocketing through short points. But it was Keys who came out on top most often, knocking off 29 winners, compared to just nine from Mertens. Mertens was also undone by six double faults.

Two of Mertens's double faults came when she was serving to stay in the first set at 6-5, the second of which handed Keys a set point. The American converted that chance, which was the first break of the day for either player.

The second set was much different, as five of the first six games went against serve. But Keys came out of that run with the break advantage, leading 4-2, and the former World No.7 eased home from there, finishing off the match with a backhand winner.

Keys will next face Viktorija Golubic of Switzerland in a fourth-round clash on Monday. Their head-to-head is level at 1-1.

"I think [Golubic is] going to be a really difficult opponent," Keys said. "I think her game is actually very well suited for grass. I think at this point everyone is feeling pretty confident in their game and playing at a high level in order to get to this point.

"I'm going to have to just continue to try to focus on my side of the net and do what I can at the highest level."