London - Roger Federer condemned Marin Cilic to more frustration in London as he repeated his Wimbledon heroics against the Croatian with a 6-7 (5/7), 6-4, 6-1 victory in the ATP Finals on Thursday.
Just four months ago and only a few miles across south London, Federer was celebrating his record eighth Wimbledon title after crushing Cilic in a brutally one-sided final.
Cilic had been hampered by a blistered foot and the Croat was reduced to tears during the match as his predicament sunk in.
In their first meeting since that All England Club showdown, Federer haunted Cilic once again as he fought back at the O2 Arena.
Having beaten Jack Sock and Alexander Zverev in his first two matches, Federer was already guaranteed to qualify as the winner of the Boris Becker group, but he didn't take it easy against Cilic.
By extending his current winning streak to 13 matches, the 36-year-old advanced from the Tour Finals group stage with an unblemished 3-0 record for the 10th time in his glittering career.
With Andy Murray, Novak Djokovic and Stan Wawrinka all absent due to injury and world number one Rafael Nadal withdrawing after his first match due to a knee problem, Federer appears to have a clear path to his seventh triumph in the season-ending event.
The prize money from Federer's win over Zverev on Tuesday took him past golfer Tiger Woods to become the world's highest earning athlete, with a career total of 84 million, according to Forbes.
But Federer is motivated by his legacy rather than the size of his bank balance and winning the Tour Finals for the first time since 2011 would be another feather in his cap at the end of a remarkable renaissance year.
When Federer missed last year's Tour Finals through injury, it seemed possible he would never recapture his former glories.
But this year Federer has been revitalised, winning the Australian Open and Wimbledon among seven titles - more than other male player over the last 11 months.
Cilic was already eliminated after two successive defeats and could have been forgiven for wanting to get the match over with as quickly as possible before heading off for his holidays.
But the 29-year-old was the more aggressive player in a tight first set which he eventually won in a tie-break.
Federer kept plugging away and the world No 2 was rewarded when Cilic made a couple of costly errors at 4-5 to surrender the second set.
That was Federer's first break of serve in the match and he quickly added a second, unloading a thumping winner down the line to take a 2-0 lead in the final set.
That was all the advantage Federer needed as he looks ahead to Saturday's semi-finals.
Later on Thursday, German third seed Zverev and American eight seed Sock will stage a winner-takes-all clash as they fight for a semi-final berth.
Both Zverev and Sock have one win from their two matches and the victor will finish as group runner-up behind Federer.
Emerging star Zverev, 20, is seeking to become the youngest Tour Finals semi-finalist since Rafael Nadal in 2006 and the first German to make the last four since Rainer Schuettler 14 years ago.
Sock hopes to be the first American semi-finalist since Andy Roddick in 2007.
Results from the fifth day of the ATP Finals at London's O2 Arena on Thursday (x denotes seeding):
Boris Becker group
Roger Federer (SUI x2) bt Marin Cilic (CRO x5) 6-7 (5/7), 6-4, 6-1
Alexander Zverev (GER x3) v Jack Sock (USA x8)
Henri Kontinen/John Peers (FIN/AUS x2) bt Raven Klaasen/Rajeev Ram (RSA/USA) 2-6, 6-1, 10-8
Jean-Julien Rojer/Horia Tecau (NED/ROM x3) v Ryan Harrison/Michael Venus (USA/NZL x8)