Midway through the fourth set, Djokovic hit a drop volley that del Potro reached for a down-the-line forehand. The ball landed near a line and was called out. Del Potro walked around the net and approached Djokovic, then the two pals smiled while chatting.
"It was (up) him to decide if he wanted to challenge or not," recounted Djokovic, the 2011 Wimbledon champion. "I said, 'Listen, if I was you, I would challenge.'"
The back-and-forth ended with del Potro playfully yanking the zipper on Djokovic's shirt.
"He's a good guy, a good friend of mine," del Potro said. "We have a fantastic relationship. But when we are playing, we want to win, for sure."
Djokovic was ever-so-slightly better, surprisingly hitting more aces, 22-4. Repeatedly, Djokovic managed to return del Potro's 130 mph serves.
There were so many important shots at important moments. One came in the third-set tiebreaker, which Del Potro led 2-1. From there, though, Djokovic won the next six points, including at 3-2, when del Potro hit one overhead smash that was retrieved, then hit another that landed in the net while Djokovic fell.
When Djokovic blocked a half-volley backhand winner to end the set, del Potro bowed his head, then pulled his white shirt over his face.
In the fourth set, with del Potro looking gassed and a step late, Djokovic broke to lead 4-3. Things were looking bleak for del Potro, but he summoned something extra to break right back, only the second time — and the final time — he would win a game served by Djokovic.
In that set's tiebreaker, Djokovic went up 6-4 with a forehand winner, earning two match points. On the first, a 25-stroke exchange, del Potro hit one of his violent, flat forehands, and Djokovic responded with a lob that landed a tad long. Del Potro waved at the ball, pleading for it to go out, then leaned over, sucking air. On the second, del Potro produced a forehand winner. He would take the next two points, too, to force a fifth set.
"It was about the nerves, and Nole handled it much better at the end," said Djokovic's coach, Marian Vajda, using his player's nickname.
Djokovic got the last break he would need when del Potro sailed a running forehand long to make it 5-3. Del Potro shielded his eyes with his left palm, and Djokovic bent over, chest heaving, knowing he was one game away. Wouldn't be easy, though. Nothing was on this day.
Del Potro pounded a forehand for a break point, and a chance to extend the match, but Djokovic answered with a winner of his own. A 123 mph service winner set up Djokovic's third match point, and this time he made it count, delivering a backhand winner down the line.
They hugged at the net, and Djokovic put a hand on the nape of del Potro's neck, consoling him.
"I know that I have been pushed to the limit today," Djokovic said. "This is where your physical strength, but also mental ability to stay tough, can decide the winner."
Murray is undoubtedly stronger, physically and mentally, today than earlier in his career, when he lost his first four Grand Slam finals.
Including his London Olympic gold medal, Murray has won 17 grass-court matches in a row, and 23 of 24. He hung in there when Janowicz was smacking 140 mph serves and taking a 4-1 lead in the third set.
At 4-2, 30-all, though, Murray hit a forehand that clipped the top of the net and trickled over, setting up a break point. Janowicz then tried a drop shot, and Murray made a long run to reach the ball for a cross-court forehand winner. That was part of a five-game run that gave Murray the third set and momentum — and pumped up the partisan fans.