Either way, the U.S. Open wins tonight.

It doesn’t get any more electric than this at Flushing Meadows when an overflow Ashe Stadium crowd must pick between two sentimental American tennis heroes, as James Blake and Andre Agassi square off in tonight’s quarterfinals.

Blake may get the stronger crowd support, even if the “J-Block” rooting section has been dismantled, as reported by The Post’s Sam Blake (no relation).

Blake has the underdog status and local ties, growing up in Yonkers, a product of the Harlem Junior Tennis League.

The wild card from Harvard is going against a legend, one of the most popular players of all time in Agassi, 35, the oldest quarterfinalist since Jimmy Connors’ 1991 run at age 39. This All-American battle royale could extend past midnight, both prone to long, baseline rallies, the specter of a five-setter very possible.

“I hope it is a very fair crowd,” Blake said. “He’s won here. He’s got so many fans. I think we both respect each other. I hope the fans take a cue from that and are cheering winners, not really cheering the errors and double faults. But I don’t know because it’s going to be a night match. People have a Heineken or two, get a little rambunctious and might scream a little too early. [But] I’m never going to be angry at a New York crowd.”

Blake has been serenaded with ovations during this fortnight, as has Agassi, who could be playing his final Open after 20 straight appearances if his back becomes problematic again.

After his five-set win over Xavier Malisse, Agassi was asked about playing his 20th straight Open.

“It means a lot more than the 19th and less than the 21st,” Agassi told the crowd.

Blake, who is 10 years younger than Agassi, recalls being 11, watching Agassi at the Open with his long hair, earring and unconventional shorts.

“I think I saw him back here when he had the lime green shorts coming out of the denim shorts,” Blake said. “I think I got a pair of those too. The denim ones, not the lime green ones. I couldn’t pull that off.”

Agassi’s come a long way from those days.

“He’s really a true gentlemen, one of the friendliest guys in the locker room,” Blake said. “That’s something that’s impressive when you don’t need to do that because you’re one of the legends of the sport. He still knows how to treat people.”

Blake’s Cinderella run has also set the Open on fire. He did not play last year’s Open, recovering from a broken neck, shingles and death of his father to cancer. He was ranked in the 200’s last month, which is why he needed a wild card to play the Open. After winning New Haven two weeks ago, his ranking climbed to 43.

“It seems surreal at the time but now it doesn’t feel surreal because I’ve done all the work,” Blake said, who is 1-3 vs. Agassi. “I’ve put in the time.”

Results

Yesterday

Men

Fourth Round

Jarkko Nieminen def. Fernando Verdasco 6-2, 7-6 (6), 6-3.

Lleyton Hewitt (3) def. Dominik Hrbaty (15) 6-1, 6-4, 6-2.

Roger Federer (1) def. Nicolas Kiefer 6-4, 6-7 (3), 6-3, 6-4.

Matches

Today

not before 1 p.m.

Mary Pierce (12) vs. Amelie Mauresmo (3)

followed by

Guillermo Coria (8) vs. Robby Ginepri

7 p.m.

Elena Dementieva (6) vs. Lindsay Davenport (2)

followed by

Andre Agassi (7) vs. James Blake