The two had played only twice previously, both going to Djokovic, but those six sets produced three tiebreakers. Djokovic won two of them, but the all-or-nothing framework of the extra session tends to favor the bigger server. The thing that makes this matchup so appealing is that Raonic has one of the best serves in the business. Djokovic, meanwhile, is the best returner of serve among ATP World Tour players. The difference in their average first serves Tuesday was 15 mph.
When Djokovic was threatening to carry off the first set with Raonic serving at 4-5, the Canadian really hit some bombs -- one of them an ace that traveled 140 mph.
"It's never smooth against Milos or against any server of his caliber," Djokovic said. "There is few guys that are serving this well. Next to him is probably John Isner and [Ivo] Karlovic. Those three guys have immense serves that have great power and great precision."
At 5-6, Djokovic managed to convert. After a lunging forehand service return, he stroked a short backhand right at the advancing Raonic's feet. The half volley was too big an ask; it did not come close to landing safely, and Djokovic exulted in the direction of his box, which includes six-time Grand Slam singles champion Boris Becker.
In the second set, it was Djokovic who served notice, hitting an unreturnable serve at 6-5 in the tiebreaker, one with an impossibly sharp angle that jumped off the court.
After an uncharacteristic break of serve near the end of the final set, Djokovic closed it out.
Afterward, he smiled and flashed a thumbs-up to the crowd. There was no emphatic celebration; there is more work to be done.
And it starts with Gulbis.
"You can see the last 12 months with his results, he's now, what, top 15, 20 in the world," Djokovic said. "After this tournament, even better. He has won against Roger, won against Tomas. I saw the match against Roger. He plays really well. I mean, he has a huge serve that, you know, if it goes in, you know, it can give him a lot of advantage over the opponent."