But while the Serb will be pleased to pick up victories in the immediate aftermath of losing his No. 1 ranking to Andy Murray
, his tension has been apparent.
Djokovic struck a ball in anger
in the direction of his coaches and near the crowd in his opener Sunday against Dominic Thiem -- had he hit a spectator, he might have been defaulted -- and on Tuesday whacked both his feet with his racket after dropping serve against Milos Raonic.
On Thursday at London's O2 Arena, a venue that has been so kind to the 29-year-old, he engaged in a rather heated exchange with umpire Fergus Murphy during a thumping 6-1 6-2 win over alternate David Goffin. Djokovic was later joined in the semifinals by Raonic, who defeated Thiem 7-6 (5) 6-3 in an encounter that decided second place in the Ivan Lendl group.
Murphy -- one of the tour's sternest umpires -- issued a time violation warning with Djokovic serving at 3-1, 30-all in the first set. In ATP tournaments, no more than 25 seconds are allowed between points, with the server almost always setting the pace.
Djokovic and Rafael Nadal
have been the two highest-profile players to intermittently exceed the limit -- recently there have been calls for a shot clock, similar to basketball -- but the 12-time grand slam winner felt he was hard done by on this occasion.
The warning came off the back of a long point and Murphy seemed to acknowledge it was the first time Djokovic went past the 25-second mark. Umpires occasionally give players a heads-up if they are close to breaking the rule but nothing was said previously to Djokovic by the Irishman.
"You're telling me something that tells me that you have no clue about the game," Djokovic said to Murphy during the changeover at 4-1.
Djokovic then turned to supervisor Tom Barnes and added: "You think that's okay? One time!"
A nod of the head from Barnes indicated that he sided with the umpire.
"Every time that I'm late if I get a so-called soft warning or pre-warning, I'll accept that and won't say a word," Djokovic later told reporters. "But I think it's fair, correct and respectful towards the player and to the game if you go over the first time ... that you at least get a heads up.
"That's all I'm asking for. I'm not the only one who has that kind of mindset and opinion about this.
"I know the rules are strict, you have to follow (them). But there should be a kind of feel, a sense for the game."
The incident was the most frustrating part of the afternoon for Djokovic, who needed only 69 minutes to win. Goffin had replaced the injured Gael Monfils, becoming the first Belgian man to play in singles at the year-end championships. Monfils withdrew Wednesday evening.
Their previous two meetings hinted of a close encounter but Djokovic's play -- even if the stats showed he committed 17 unforced errors and hit only seven winners -- and a shaky Goffin led to the lopsided result.
"Yesterday I was feeling a little bit on holiday," Goffin told reporters. "And all of a sudden someone tells you, 'You have to play in front of 15,000 people against Novak.
"It's not easy to come out on the court and play your best. It was a strange feeling this week."
Djokovic knows he will regain the No. 1 ranking if he wins the title but, as unlikely as it is, he will also do it if Murray fails to reach the semifinals.
"That's obviously something you wish for, to have everything in your hands, not to depend on other players," Djokovic said.
"Everything has been going in a positive direction. I've been playing better and better as I proceed in the tournament. It's the last couple of matches of the year hopefully. One thing is for sure: I'm going to give it all on the court and see what happens."
Murray is 2-0 and atop the John McEnroe group, though hasn't officially progressed. On Wednesday the Scot won the longest three-set match in this tournament's history
, beating Kei Nishikori in three hours, 20 minutes.
Both Murray and the Japanese player (1-1) are bound to be jaded Friday when they respectively face Stan Wawrinka (1-1) and Marin Cilic (0-2), US Open champions present and past.
Raonic, the reigning Wimbledon finalist from Canada, hit 14 aces and didn't face a break point against Thiem. But the free swinging Austrian had his chance.
Leading 4-2 in the tiebreak, Thiem benefited from a short forehand on his favored forehand. Instead of punishing Raonic, however, he centered the ball, the rally continued and Thiem produced a backhand error. It was the turning point as Raonic rallied.
Raonic could play Murray in the semifinals and thus potentially end his year-end No. 1 hopes -- two weeks after the world No. 4's walkover in Paris handed Murray the No. 1 spot.