Two-time Western & Southern Open finalist Angelique Kerber led a host of winners into the second round of the event, including Elise Mertens and Paula Badosa, on Monday evening in Cincinnati.

The former World No.1 Kerber of Germany, who reached the championship match at the tournament in 2012 and 2016, rolled past Maria Sakkari of Greece 6-2, 6-2 in a 1-hour, 9-minute battle between two of the highest-ranked unseeded players in the draw.

The Center Court nightcap between two of this year's Grand Slam semifinalists (Sakkari at Roland Garros, Kerber at Wimbledon) ended with Kerber taking a 3-1 lead in their head-to-head, despite Sakkari having won their most recent clash earlier this year at the Grampians Trophy in Melbourne.

Kerber eases past Sakkari in Cincinnati first round: Highlights

The victory continues a run of excellent form for Kerber, who is now 11-1 in her past 12 matches. Kerber won her first title in three years on home soil at Bad Homburg, which the former Wimbledon champion followed up with her run to the semifinals in London before being ousted there by eventual champion Ashleigh Barty.

Keys to the match: Three-time major champion Kerber executed a number of her classic crouching shots to change direction on a dime, and she particularly excelled against the second serve of Sakkari, winning nearly 81 percent of those points.

The return game served her well during a first set which was more closely-contested than the score line implies. The pair exchanged breaks twice before Kerber took command, breaking Sakkari in the Greek's final two service games of the set to grasp the opening frame. Kerber swept through the second set to finish.

Next up for Kerber: The German will try to keep her hopes for another trip to the Cincinnati final alive when she meets one of the top players in the field and a frequent rival in the second round, No.4 seed Elina Svitolina of Ukraine.

Svitolina leads their head-to-head by 9-5. They played for the first time in three years earlier this season on the indoor clay of Stuttgart, where Svitolina won in straight sets.

Paula Badosa of Spain eked out a first-round win on Monday.

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Mertens eases past Podoroska; Badosa fends off five match points to beat Martic

Earlier on Monday evening, No.15 seed Elise Mertens eased into the second round of the Western & Southern Open, while Paula Badosa saved five match points before winning a marathon opener on a rain-plagued Monday evening in Cincinnati.

Mertens of Belgium moved past Nadia Podoroska of Argentina 6-3, 6-4 in an opening-round win at a tournament she has previously experienced much success. Mertens was a semifinalist at the tournament last year (when it was played in New York) and a quarterfinalist in 2018.

The pair had faced off only once before, at an ITF Challenger event in Victoria, Mexico in 2015, and Mertens won in straight sets. In their first tour-level meeting, it was Mertens who prevailed again in an hour and 40 minutes of play, converting three of her six break points.

Effectiveness with the second serve was the key difference between the two. Mertens won 55 percent of points she started with that shot, while Podoroska's success rate was at a less hefty one-third.

Despite frequent powerful forehands by the Argentine, it was Mertens who controlled the match on return for the most part. Back into the second round, Mertens will next meet either former US Open champion Samantha Stosur or Elena Rybakina, one of the highest-ranked unseeded players in the field.

Badosa was pushed to the brink by Petra Martic of Croatia. The Spaniard needed 2 hours and 34 minutes to quash the challenge from Martic, 4-6, 6-4, 7-6(9).

After splitting the first two sets, Martic broke serve in the very first game of the third set, and maintained that advantage up to 5-4, where she served for the match and held three match points. But Badosa got the break back right when she needed to, leveling the set at 5-5, then grabbed two match points of her own on the Martic serve at 6-5.

Martic, however, fended those off, and the pair entered the tiebreak, where at 6-6, after Martic's fourth match point, a 20-minute rain delay took place. After that nerve-wracking pause, the pair returned, where each player held one more match point before Badosa converted her third chance at 10-9 and sank to her knees in delight.

Badosa will face one of the top seeds in the next round: No.3 Aryna Sabalenka of Belarus.

Americans move on in Cincinnati

A trio of Americans claimed late-night wins on home soil at the event on Monday evening, led by No.13 seed Jennifer Brady, who defeated Russia's Ekaterina Alexandrova 6-3, 7-6(3) in their first-round clash.

Brady, this year's Australian Open finalist, was never broken in the 83-minute affair as she picked up her first win since Roland Garros. Brady will next face 2017 Roland Garros champion Jelena Ostapenko.

Alison Riske had an even easier time as she swept past teenaged Canadian Leylah Fernandez 6-2, 6-2 in 80 minutes. Riske won 14 of Fernandez's 17 second-service points.

And an all-American clash went the way of Shelby Rogers as she advanced past Danielle Collins. Due to a left hip injury, Collins retired from the match with Rogers leading 6-4, 2-1.