First came the big win. Now comes the even bigger run.

How big? American qualifier Taylor Townsend has come too far to sell herself short, saying she’s going to take it all the way.

This coming on the heels of Thursday’s first ever upset of a top-10 foe, and in the afterglow of Saturday’s 7-5, 6-2 U.S. Open win over Sorana Cirstea that vaulted her into the round of 16.

It’s the first time the 116th-ranked Townsend has reached the second week of a Grand Slam. And with the women’s field suddenly thrown wide-open after a spate of upsets — including her own win over Wimbledon champ Simona Halep — she’s hungry for more.

She showed that with her play, and her “got to eat” celebration after match point.

“I made it up in my mind before I came. I was going to qualify — nothing was going to get in my way of that,” Townsend said in an on-court TV interview. “I was like, ‘I’m here, I’m going to make it count.’ ”

Townsend will face Canadian teen Bianca Andreescu, who beat Caroline Wozniacki 6-4, 6-4. And with the Nos. 4, 7 and 9 seeds all already gone from her top half of the draw, how far can Townsend take this?

“Like I said, I’m here now,” Townsend said. “We’re going to ride this thing all the way.”

Saturday marked the fifth straight match Townsend came from behind to win. She found herself down 3-1 and trailing 30-0 in the next game before the tide turned. Or more accurately, Townsend turned it.

With Cirstea comfortable when allowed to sit back and control the match, Townsend went on the attack as she had against Halep. She charged the net to win the next two points on backhands, and broke on a backhand winner. She took six of the next eight games, and the first set.

Townsend won 47 of 75 points at the net, and threw Cirstea all off her rhythm. She was 33-of-53 in serve-and-volley points, while her foe didn’t have one. The tactic worked against Halep, and against another Romanian on Saturday.

“Honestly, I didn’t know that many people had my phone number,” Townsend said of the flood of congratulatory calls when she beat Halep. “But yeah, these are new feelings. I made third round before, but it wasn’t in the States, it was in another country.

“I got a lot of messages. It was a lot of love. My phone started dialing 9-1-1 by itself — I don’t know what that was about. I just tried to keep my head on straight. My coach and I talked about … continuing what I did the last round and trying to get better.”

Up next is No. 15 Andreescu, also into the second week of a major for the first time despite a shoulder injury that cost her months.

“I know what to expect. I know she loves coming to the net — she has incredible volleys. I’ll for sure work on some passing shots during my practice,” said Andreescu, who faced Townsend on Friday in doubles. “There aren’t a lot of players that play like her, so I’m going to do my best to figure out what to do when she comes to the net.”