London: Novak Djokovic crushed David Goffin 6-1, 6-2 at the ATP Tour Finals on Thursday as the world number two kept his foot on the gas in the race to finish the year atop the world rankings.
Djokovic had already qualified for the semi-finals as group winner, but the Serb was keen to keep the momentum going in his bid to overhaul world number one Andy Murray and he took just 69 minutes to demolish Goffin at London's O2 Arena.
Joining Djokovic in the last four is Milos Raonic, who defeated Dominic Thiem 7-6 (7/5), 6-3 to become the first Canadian to reach the semi-finals of the Tour Finals.
Djokovic has been in a prolonged slump since winning the French Open for the first time in June, sparking rumours about his private life and questions about his recent involvement with a 'spiritual guru' as he lost the top ranking to Murray.
But the decline is all relative as the 29-year-old has now won 21 of his last 22 matches at the Tour Finals, keeping him on course to win the tournament for a fifth successive year and record-equalling sixth time in total.
It is also the fourth time in the last five years that Djokovic has won all three of his group matches at the Tour Finals.
Djokovic is now 70 points ahead of Murray in the ATP's 'as it stands' rankings, although he already knew winning the tournament would give him the year-end pole position whatever happened against Goffin.
"I'm very glad my game is going in the right direction. Today I felt the most comfortable so far in the tournament," Djokovic said.
"I felt like I increased the quality of tennis compared to the other matches.
"I'm looking forward to the semi-finals on Saturday."
Murray faces Stan Wawrinka in his last group match on Friday knowing a victory would guarantee he qualifies as group winner, thus avoiding a clash with Djokovic before the final.
Goffin was a late replacement for the already eliminated Gael Monfils, who pulled out of his last group match to avoid aggravating the rib injury that has troubled him for several weeks.
The Belgian, up to a career high 11th in the world rankings, had been paid £80,000 ($99,000) to hang around the O2 Arena all week as one of the tournament's on-call substitute players, but even that sum might not have made up for acting as a punch bag for Djokovic.
Djokovic had won all four of his previous encounters with Goffin and he quickly took control again with a break in the fourth game of the first set.
Not for the first time this week, Djokovic cut a tetchy, brooding figure and after being given a time violation for taking too long between serves he had an animated conversation with both the umpire and tournament supervisor as he complained about not being given a warning first.
Controlling his emotions was proving tricky, but Djokovic was in complete command of his play and he broke again to take the first set with ease.
Djokovic was in ruthless mood and breaks in the third and fifth games of the second set effectively ended the contest.
In Thursday's evening session, Raonic maintained his remarkable success in London this year with a powerful display that secured the runners-up spot in the group.
The world number four had enjoyed impressive runs to the Wimbledon and Queen's finals on the other side of the capital in the summer and he saw off Thiem in 90 minutes to reach his ninth semi-final of the year.