"I wasn't the better player today" - admits Isner following upset win over Rublev

With very little playing time on clay this season, it came as a huge surprise when John Isner stunned sixth seed Andrey Rublev on Thursday to secure his spot in the quarterfinals of the Madrid Open.

The big-serving American put on a consistent performance to outlast the Russian 7-6(4) 3-6 7-6(4), ending Rublev's run of reaching at least the quarterfinals in all seven of his ATP tour-level appearances this season.

“I’m very happy,” Isner said after the match. “I wasn’t the better player out there today; I did win the match. My serve kept me in it. There’s a reason he’s won so many matches this year.”

With his rank falling to World No.39, this win marks Isner's first Top 10 win since he defeated Alexander Zverev at the Laver Cup in 2019.

"It's a nice feather in my cap right now with my ranking being a little bit lower," Isner said. "I haven't played much since the tour stopped last year. I think this is my only seventh event. I haven't had many matches. But to beat a guy like that, maybe being a little bit undercooked, is a very special moment for me."

The towering American also mentioned his preference for the Madrid courts, citing it's similarity to the hard courts on which he has had a lot more success.

"It is my favorite clay court probably," Isner said. "It has an indoor feel even though it's not fully indoors. It's got a great sound to it. The court is fast. To me it doesn't seem like there's too much clay on the court so, of all the clay courts I play on, it plays closest to a hard court of any of them. The altitude in Madrid just really helps my serve. The ball goes through the air very fast. You put all those things together, it's a good recipe for me to do some damage on serve."

Awaiting Isner in the quarterfinals is Dominic Thiem, as the Austrian ousted Alex De Minaur earlier in the day.