At midnight, a few fans had given in to the end of summer and begun to leave the Arthur Ashe Stadium.
By 1 a.m., there was a steady flow at each break in play.
By 2 a.m., the upper bowl was filled mainly by night cleaners ready to go to work.
When it ended at 2:26 a.m., taking Canada's last Grand Slam hopes of the season with it, there were still a few thousand die-hards left.
As we edged past several endurance records, Milos Raonic and Kei Nishikori were slugging it out on American tennis' greatest stage. 'Slugging' is the proper word. This Round of 16 encounter was an epic battle of attrition in which both men frequently flagged, but neither would fall.
Though suffering from foot blisters and the lingering effect of a toe infection, Nishikori was the man who still had something left as it edged beyond the four-hour mark. He won 4-6, 7-6(4), (6)6-7(8), 7-5, 6-4.
The end time tied it for the latest match in U.S. Open history. The four-hour-and-nineteen minute duration made it the longest match at the tournament this year.
Asked afterward if those superlatives mattered to him at all, Raonic said, "Not in the slightest."
From the start, it was a contest matching Raonic's power and Nishikori's ability to chase. As it stretched on, the Japanese began to dominate on his serve. Very little was working very well for the Canadian, but he was able to jury rig a strategy that gave him a chance.
By the end, Raonic was utterly spent. In the final few games, he made little effort to pursue balls that weren't in arms reach. These athletes spend much of their time working on conditioning, but this match proved how difficult it is to prepare a 6-foot-5, 216 lb. man to run a marathon.
"You find parts where you're not normally sore are getting sore," Raonic said.
Once he was broken in the fourth set, you could feel the will ebbing out of him. Nishikori was from that point on unbeatable on his serve. Raonic simply couldn't match him in endurance. The Canadian did not have a single break-point opportunity after the second set.
That made it an even more stalwart performance. Though Eugenie Bouchard captured much of the attention from Wimbledon on, Raonic proved here that he is more than a big serve. He's a big serve with a heart.
The most encouraging thing of all – his body let him down, rather than his head. His body can be fine-tuned. The head you have to be born with.
For the first time this year, he was the last Canadian standing at a Grand Slam. It won't feel like much come Tuesday morning, but it's something.
There was a telling moment about his new place in the tennis world during a press conference earlier in the day with Stan Wawrinka. Someone mentioned that Raonic had commented that Wawrinka's win at the Australian Open had given everyone outside the Big Four hope. Wawrinka shrugged off the premise, with a caveat.
"If you look at who's won the majors since then, it's still the same (people). For Milos, it's a little bit different. He's improving a lot. He's still young. He's there."
That's a pretty good tagline on Raonic's 2014 Grand Slam season: 'He's there.'
A third-round, a Round of 16, a quarterfinal and a semi (at Wimbledon). The semi was his pre-season goal. He's right there. He just needs a bit of luck.
Raonic talked repeatedly during the first week about "courage," and sustaining himself when he isn't at his sharpest.
On that score, the third set may stand out as one of the finest examples of his career. Over the course of two consecutive service games, he survived eight break points. By contrast, Nishikori lost only seven points on his service the entire set.
And yet Raonic still found a way to muscle through and get to a tiebreak. Once there, he continued his stunning run in those pressurized moments, overcoming the Japanese 8-6.
In defeat, the 23-year-old Canadian showed his remarkable resilience.
He may not yet be a Grand Slam champion, but tournament-by-tournament, he's building the skillset and experience that will allow that to happen one day soon.