London: Defending champion Novak Djokovic trounced stand-in David Goffin 6-1, 6-2 for a clean sweep of his group at the ATP World Tour Finals on Thursday but still looked far from happy as he picked a row with the chair umpire.
Belgium's Goffin pocketed $179,000 for his brief appearance, courtesy of an injury that forced Gael Monfils to withdraw on Wednesday, earning almost $60,000 for each game he won in a no-contest lasting 69 minutes.
It was poor value for the O2 Arena crowd and nothing more than a gentle workout for Djokovic who did his best to enliven the flat atmosphere by having a lively exchange of views with umpire Fergus Murphy after being given a time violation.
Djokovic, who had already won the group after wins over Dominic Thiem and Milos Raonic, was given the warning for going over the 25-second time limit while serving at 3-1.
"You have no clue about the game," an irate Djokovic told Murphy at the changeover before turning to continue the debate with tournament director Tom Barnes.
Djokovic, whose year has tailed off since he claimed the French Open in June and whose position as world No. 1 was usurped by Andy Murray last week, has been prickly in London and argued with a reporter during a news conference on Sunday.
The Serb, who could snatch back the world No. 1 ranking from Murray if he wins a fifth successive title in London, did not let the flare-up effect his progress and broke for the second time in the next game.
World number 11 Goffin was coming in cold and never really got to grips with the court surface, the unique setting or his clinical opponent and despite some occasional flashes of his silky shot-making he was never in it.
Djokovic will face the runner-up of the John McEnroe group in the semi-finals.
On Wednesday, Stan Wawrinka out fought Marin Cilic to keep alive his chances of qualifying for the semi-finals at the ATP World Tour Finals here.
Third seed Wawrinka, who saved one set point in the first set, earned a confidence boosting 7-6 (7-3), 7-6 (7-3) victory over seventh seed Cilic in one hour and 58 minutes in Group John McEnroe.
"It was a great match," said Wawrinka. "I'm really happy with the way I played in general. It was a tough match, for sure - two tie-breaks. I think the level was really high... I think I was moving great. It was a great victory for me."
Wawrinka will next face top seed Andy Murray. Murray leads Wawrinka 9-7 in their head-to-head, with their lone meeting in 2016 coming in the Roland Garros semi-finals. Wawrinka won their round-robin clash at The O2 last year 7-6 (7-4), 6-4.
