Sports

Nadal exhibits old fire in Showdown defeat

An athlete seeking to stage a successful comeback from injury must undergo a series of tests in competition to see how the injury responds.

For Rafael Nadal, a comeback from knee tendinitis that cost him seven months is not yet complete, and likely won’t be so until he can sustain a high level of play on hard courts. But in an encouraging sign, Nadal came through his first (albeit unofficial) hard-court match feeling good.

“The knee answered [well]. I ran [around a lot],” Nadal said after last night’s BNP Paribas Showdown at the Garden, where he was defeated in an exhibition match by Juan Martin del Potro, 7-6 (7-4), 6-4.

Indeed, Nadal moved well despite not being 100 percent, leading the first-set tiebreaker 4-2 before del Potro stormed back to win. Nadal was broken in the fifth game of the second set and could not get back on serve.

Nadal said that he will do all he can to make sure the knee pain he’s still feeling is tolerable, and is encouraged that last week’s tournament result, when he won the Mexican Open Saturday in Acapulco over Spanish countryman and world No. 4 David Ferrer, 6-0, 6-2.

“The only thing I can do is do all the right things to be ready,” Nadal said. “If I can compete and run with no limitation on my movement, that’s a lot for me. That happened … in Acapulco, and that gave me a lot of positive feeling and confidence in myself.”

* In the first match last night, world No. 1 Serena Williams posted a 6-4, 6-3 victory over world No. 2 Victoria Azarenka.

The tennis was completely serious for a set and a half, but at 3-all in the second set and Azarenka facing a break point, the levity began as RedFoo, the rumored boyfriend of Azarenka and half of the pop duo LMFAO, played a point against Serena, needing four attempts to successfully serve.

The match also was replete with catcalls from the audience, with one fan yelling a marriage proposal to Serena and another screaming out, “I’m sexy and I know it,” referring to the LMFAO hit.

Both players said they were honored to play on the Garden stage.

“I felt so much love from the fans,” Azarenka said. “It’s an incredible feeling to play at Madison Square Garden.”

jdemarzo@nypost.com