Sloane Stephens doesn’t like to say she’s defending her title, feeling the phrase misses the mark. The quirky Californian just so happens to be doing a great job of it so far.

With top seeds falling around her, No. 3 Stephens motored into the quarterfinals Sunday. In winning her 11th straight match in Flushing, she showed the speed of the 7 train on two rallies when she raced from the net to behind the baseline to make impossible gets.

The 6-3, 6-3 trouncing of Belgium’s No. 15-ranked Elise Mertens sets up a rematch of last year’s Open quarterfinal against Latvia’s Anastasija Sevastova. Stephens rallied from a 3-1 third-set deficit to win in a tiebreaker last September.

The draw is opening up for Stephens, who is the only one left of the top five seeds. No. 1 Simona Halep, No. 2 Caroline Wozniacki, No. 4 Angelique Kerber and No. 5 Petra Kvitova have been eliminated.

“I think defending a title is super tough,” Stephens said. “I think the expectation to come in here and win the tournament is just ridiculous. Defending a title isn’t defending. If you were to play the same people in a row again and beat all of them again, that would be defending your title. You’re playing a whole new draw.”

Stephens is three wins away from a second Open trophy but admitted doesn’t see the first one.

“Who cares about the trophy?” she said. “I’ve only seen my trophy like once or twice. It’s at my grandparents’ house [in Fresno, Calif.] It’s in their dining room. They see it every morning, show all their friends.”

Stephens delighted the Arthur Ashe Stadium night crowd with her breakneck speed. On one venture, she was at the net to retrieve a drop shot and chased a lob well behind the baseline, bending over to pick it out of the asphalt. Her return was smashed back at her, and she defensively batted the ball back for a winner.

She performed the same trick later with her forehand, connecting on a crosscourt passing shot after racing all the way back.

“The crowd went crazy,’’ Stephens said.

But she won’t practice those athletic trick shots.

“Run back there, hit it, hopefully it goes in,’’ she said. “I don’t practice that. I think it makes it unnatural.”

What looked perfectly natural was Stephens’ first serve as she got in 83 percent of them against the overmatched Mertens, who had lost in the first round of the Open the past two years and was the first Belgian to reach the fourth round of a Grand Slam since 2010.

Now Stephens, who secured match point with a deft passing shot from deep in the backcourt, must worry about a Latvian who nearly ran her out of the Open last year. If she gets by Sevastova, then it could be the semifinal match of the year when she could be in line to face Serena Williams, who missed last year’s Open giving birth.

Stephens said she started the Open a bundle of nerves, but they are subsiding.

“I’m playing solid — I just have to keep that in mind,” Stephens said. “Being the defending champon is crazy. Then to follow that up and do well again, I think it’s something to really get behind.”