Maybe it’s the cheesecake.

Simona Halep, the U.S. Open’s fifth seed, has made a habit of sampling the cheesecake in the players’ dining room at the National Tennis Center every day. Satisfies the sweet tooth, energizes her scampering legs. Lets her run and run and run.

When Lucie Safarova walked onto the Arthur Ashe Stadium court Thursday morning for her match against Halep, she knew one thing for sure: The ball would come back, always.

Halep is a wall. The Romanian is quick afoot and runs down every ball. What she lacks in power, she makes up for in placement. Her serve isn’t a rocket, but it’s effective. In long rallies, she waits for her opportunity, or for her opponent to make a mistake. Her 6-3, 6-4 win over Safarova was classic Halep.

There are two statistics that bear out her strategy and define her second-round win. She hit only nine winners but made only 20 unforced errors. Safarova hit 16 winners but made 44 errors.

“I knew that I have to be strong on my legs because she is there and she hits the ball pretty strong,” Halep said. “I think I was very, very good on my legs and I could return every ball. I missed some, but also, I did some good points. Gives me confidence that I can beat her. Hopefully for the next round I can be better. I will be like more confident on court.”

advertisement | advertise on newsday

Safarova, unseeded but always dangerous, knew she couldn’t afford to get into endless rallies with Halep and that she would have to serve well. Trying for winners to end rallies quickly didn’t work, and the serve just wasn’t there.

“She’s a great defender. She gets tons of balls back,” Safarova said. “Once you aren’t pressuring her, she takes [the advantage] and uses her lines. Today, I made way too many mistakes to beat her. My serve wasn’t working as well. I’m more of an offensive player that likes to take the shots earlier, so it puts a little bit more pressure on myself. I think I rushed some balls too early.”

Halep is 24, and her game is picking up steam. She’s won three titles this year, with big wins at Madrid and Montreal and a home country win in Bucharest after skipping the Olympics over concerns about the Zika virus. She is 21-3 since the start of the French Open, with losses to Samantha Stosur at Roland Garros and Angelique Kerber at Wimbledon and Cincinnati. She beat Dominika Cibulkova in the Madrid final and Madison Keys in Montreal after defeating Kerber in the semifinal.

Halep has been knocking on the Grand Slam door the last three seasons. She lost to Maria Sharapova in the 2014 French Open final. Last year at the Open, she lost in the semifinals to eventual champion Flavia Pennetta.

As she settles into the routine of winning in New York, she continues to do the very New York thing — cheesecake.

@NewsdaySports

“I had yesterday and I will have one now after the lunch,” Halep said, smiling. “I like to have some nice routine with this food.”