Just five games into the Citi Open final Sunday, Nick Kyrgios clutched at the middle of his back after a point. Soon, he was holding onto the chair umpire's stand while trying to stretch.

When the opening set ended, he was flat on the ground, getting treatment from a trainer. Eventually, after 1 1/2 hours of play, Kyrgios was wincing in pain — because he was lifting the champion's trophy at the hard-court tournament.

Kyrgios overcame a bothersome back and used two of his 18 aces to close things out, edging No. 3 seed Daniil Medvedev 7-6 (6), 7-6 (4) to win his second title of the year and move his ranking back into the top 30.

"This has honestly been one of my favorite weeks of my life, to be honest. I've made massive strides," said Kyrgios, who warmed up for matches by taking on kids in pingpong in the players' lounge. "A week to remember."

Kyrgios, who came into the U.S. Open tuneup event ranked just 52nd, followed up his thrill-a-minute semifinal victory over top-seeded Stefanos Tsitsipas a day earlier with a much more mundane triumph in the final.

There were zero break points for Kyrgios or Medvedev all match. The difference came down to Kyrgios' superior play in the two tiebreakers. He trailed 4-1 and 5-2 in the first, before coming back, helped when Medvedev pushed a forehand wide on set point.

In the second, Kyrgios only fell behind once, at 3-2, but used a combination of three aces, a 140 mph service winner and a flubbed forehand by Medvedev to end things. On match point, Kyrgios revived a bit he's been doing this week, going to "consult" a spectator before uncorking a serve. After huddling with a woman in the front row Sunday, he hit a 118 mph ace, then dropped his racket and fell on his back.

Earlier Sunday, Jessica Pegula — a 25-year-old American ranked 79th, whose parents own the NFL's Buffalo Bills and NHL's Buffalo Sabres — won her first WTA title, defeating Camila Giorgi 6-2, 6-2 in the women's final.

It seemed to be touch-and-go for Kyrgios early on: He repeatedly grabbed his back or attempted to flex it, either between points or while on the sideline between games.

Still, the 24-year-old Australian managed to hang in there, mainly relying on his big serve — which reached 140 mph in the second set — to get past the 10th-ranked Medvedev and improve to 5-1 against top-10 foes in 2019.

"The career he's going to take off on is going to be pretty special," Kyrgios said about Medvedev, a 23-year-old Russian. "He's a great example for anyone who wants to pick up a tennis racket."

This was Kyrgios' sixth career title. The other one this season came at Alcapulco, where he saved match points against Rafael Nadal. This time, Kyrgios saved a match point against Tsitsipas.

Never seems to make things easy on himself.

As usual, Kyrgios drew cheers for some of his more unusual shot selections. There was an underarm serve that won a point in the second set. There were a couple of unnecessary — yet appreciated — 'tweeners, too, one of which produced a lob that Medvedev tried to get back over the net with a between-the-legs shot of his own, but his landed out.

Kyrgios is nothing if not inconsistent, something he sometimes pledges to work on. He arrived in Washington with a record of only 13-10 for the year.

He's still only made it past the round of 16 at two tournaments all season — but at least he won the titles each time.

"We all know how Nick can play when he wants to win," Medvedev said. "This week, I think he wanted to play, and it was tough."