ACAPULCO, Mexico – No.2 seeded Sloane Stephens booked her spot in the semifinals at the Abierto Mexicano Telcel with a commanding win over Naomi Osaka, 6-3, 7-5.

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It had been a dream week for Osaka in the Mexican paradise of Acapulco – the Japanese wildcard made her first ever WTA quarterfinal and in the last round ousted Mariana Duque-Mariño in straight sets after saving a set point in the second.

But lying in wait in the quarterfinal was big-hitting American Sloane Stephens, who already knew what to expect from the 18-year-old.

“I was playing a girl who is younger than me who’s been playing really well lately,” Stephens said. “I knew it was going to be tough going into it.”

Stephens got the first break of the tense first set at 4-3. Osaka almost hung on fiercely in the five-minute game, running around her backhand to blast her huge forehands and saving two break points, but to no avail. Stephens grabbed the next two games to close out the set at 6-3.

Osaka grabbed the first break of the final set, but Stephens broke back in reply, keeping them level until she broke Osaka at 5-3. The Japanese edged her way back after a nervy game from Stephens while she was serving for the match at 5-4 – Stephens was broken at love after a double fault on break point. She righted the ship when it counted, though, and broke for the match at 7-5.

With her title in Auckland earlier this year and a semifinal appearance here in Acapulco, this has been Stephens’ best start to the season since 2013.

“It’s only February, so there’s a lot of tennis to be played this year,” the American said. “I’m happy that I’ve had such a good start so I’m just trying to keep the momentum going.”

Awaiting Stephens in the next round is No.8 seed Yanina Wickmayer, who is into her first WTA semifinal of the year after a straight sets win over Anastasia Pavlyuchenkova, 6-3, 7-6(3).

Though Yanina Wickmayer leads their head to head 2-1, the record hides just how their encounters have been – all of their previous matches have gone to three sets. This time, Pavlyuchenkova looked like she had an edge; she hasn’t lost a set here in Acapulco and was into her third quarterfinal of the year while Wickmayer had to come back from a set down in each of her previous matches.

The Belgian player is into her first WTA semifinal of the year and her first since winning the Tokyo International in 2015.

On the other side of the draw, Dominika Cibulkova faced her first big test at Acapulco against No.7 seed Johanna Larsson.

Cibulkova has had a smooth ride to the quarterfinals so far – she won her first round match in a 6-0, 6-0 beatdown and received a walkover in the last match as a result of Victoria Azarenka’s withdrawal. But it turned out to be a blessing in disguise for the Slovakian player.

“It helped me today to be more ready because yesterday I had the day off,” Cibulkova said.

“Today was really tough physically – I had the first match of the day and it was really humid and hot. So yeah, I think it really helped me to have yesterday off.”

Cibulkova was in trouble early on, still adjusting to the tough conditions and dropping the first set 6-3. It was just a matter of time before the former Top 10 Slovak got going, upping her serves and finding the lines with her booking groundstrokes to take the second 6-2. Larsson handed Cibulkova match point while she was serving to stay in the match at 5-3, then helped her seal the match burying a return into the net, 3-6, 6-2, 6-3.

Up next Cibulkova is set to face Christina McHale in a rematch of the 2014 Acapulco final. The unseeded American defeated Mirjana Lucic-Baroni 6-4, 6-7(6), 6-2.

“It’s going to be a really tough match,” Cibulkova said. “We are already in the semifinals and we’re all feeling the heat. The more ready player is going to win tomorrow.”