Two former World No.1 players who have Wimbledon titles on their resumes picked up swift victories in the first round of the inaugural bett1open on Tuesday.

On home soil in Berlin, Germany's top-ranked player Angelique Kerber defeated Japanese qualifier Misaki Doi, 6-2, 6-1, to book her spot in the second round.

"It was a really solid match," Kerber said, in her post-match press conference. "It’s never easy to play a first match on grass courts, especially against a lefty as well. So I’m really happy about my performance and how I started the grass-court season."

Later in the day, No.6 seed Garbiñe Muguruza of Spain joined her in the second round of the grass-court event, after easing past Romania's Sorana Cirstea, 6-3, 6-2.

Berlin marked the first meeting between Kerber and Doi since a fourth-round showdown at 2016 Wimbledon, and Kerber has now improved her win-loss record against Doi to 6-0.

That head-to-head includes a famous first-round clash at the 2016 Australian Open, where Kerber saved a match point against Doi, and then went all the way to her first Grand Slam title.

"[That] was the match which I turned around and was able to win my first Grand Slam, so of course you will have this match always in your mind," Kerber said. "But every match starts from zero, so I was more focused on the match today, playing against her on grass-court. She played good matches in the qualies, so it’s never easy to play against someone who played a few matches already."

This time around, 2018 Wimbledon champion Kerber was in complete control, hitting 23 winners to just 10 unforced errors, and saving all three of the break points she faced, as she eased to a 60-minute victory.

"It’s really nice being back on grass, that’s my favorite surface," Kerber said. "It’s never easy to start a grass-court season because it’s completely different from the clay courts, but it’s great for me to play in Germany, it’s always really special. That gives me a little bit more motivation."

Kerber reeled off the first seven points of the match en route to finding herself up a double-break at 3-0, ending that run with a divine rally backhand winner. Kerber saved a break point and gritted out a tough hold for 4-0 before Doi at last got on the scoreboard, courtesy of an overhead winner for 4-1.

At 5-1, Doi saved two set points with a forehand winner and a winning dropshot respectively, and held serve. But Kerber was not to be denied, and confidently served out the opening frame at love.

A break in the first game of the second set kicked off a similar run for Kerber as she again leapt to a 4-1, double-break lead. The former World No.1 needed to save two break points in the next game, but got out of that jam before breaking Doi for a third time in the set to close out the win.

Kerber will now take on another former World No.1 and multiple-Grand Slam champion in the second round: Victoria Azarenka, who defeated another German, Andrea Petkovic, earlier on Tuesday.

"I will try to play my game, and try to take another chance, and play as many matches as I can before I go to Wimbledon," Kerber said, looking ahead to her 11th meeting with Azarenka (with Azarenka leading the head-to-head 9-1). "It’s another good match at a high level, and this is why I’m here. The draw is really strong, so it’s good to have another good match."

2017 Wimbledon champion Muguruza also kept an undefeated head-to-head alive with her one-hour and 19-minute win. The Spaniard is now 4-0 lifetime against Cirstea.

"Very pleased," Muguruza said on court, after her win. "You never know how it’s going to go in the first match, especially on grass after two years, so I’m very excited to win in two sets against Sorana. We’ve played many times, and it’s always difficult."

In the final first-round match of the tournament, Muguruza advanced after leading Cirstea in winners by 15 to 12, and converting six of her 14 break points. Muguruza ended a two-match losing streak as she improved her stellar season win-loss record to 24-8.

Cirstea came undone with 35 unforced errors in the match, but despite the loss, the Romanian is still having a resurgent 2021. Cirstea won her first WTA singles title in nearly 13 years in Istanbul, and reached the round of 16 at Roland Garros last week.

Muguruza bests Cirstea in first round: Berlin Highlights

2021 Berlin

Muguruza won all of her 14 first-service points in the opening set, in which she took control by winning a critical 3-3 game, which went to deuce seven times before Muguruza converted her fourth break point of the game. Muguruza broke a second time for good measure at 5-3 to clinch the one-set lead.

"I guess I was feeling my serve today, and on this surface, it’s super important," Muguruza said.

Muguruza cruised to a 4-0 lead in the second set as well before she double-faulted on break point of the next game, dropping serve for the first time. The last five games of the clash went against serve as Cirstea opened up on returns, but Muguruza at last wrapped up the win with a backhand winner down the line.

Muguruza will next face Elena Rybakina of Kazahstan in the second round. Rybakina needed an hour and 43 minutes to outlast Shelby Rogers of the United States in their first-round tilt, 2-6, 6-3, 6-4.

World No.21 Rybakina, who reached her first Grand Slam quarterfinal last week at Roland Garros, saved all four of the break points she faced in the final set as she edged Rogers in their battle.