Wide-eyed Wallabies Bernard Foley and Will Genia enjoyed front-row viewing as six-time champion Roger Federer notched yet another milestone at the ATP World Tour Finals in London.
In town for Australia's grudge match against England at Twickenham, Foley and Genia nestled in between Federer's father Robert and British adventurer Bear Grylls as the Swiss superstar returned to haunt Marin Cilic with a tough three-set win.
Already assured of a record 14th semi-final appearance at the season-ending showpiece, Federer clinched top spot in his four-man group with a 6-7 (5-7) 6-4 6-1 victory on Thursday to reach the last four unbeaten for an incredible 10th time.
Federer was frustrated not to have converted any of his five break-point chances until deep in the second set amid a run of five straight games to take command of the match.
He raced through the deciding set with two more service breaks to repeat his crushing victory over Cilic on London's nearby grass courts in this year's Wimbledon final.
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"I was also a break point down early in the second set so I'm happy I found a way out of it," Federer said before posing for selfies with Foley and Genia.
"I played really well so I'm happy to be playing this level right now."
The 19-time grand slam champion admitted it was a strange feeling knowing he wouldn't be going home even if he had lost, but said the unusual scenario also freed him up to play his best tennis when he needed it.
"I tried to relax a little bit," he said after completing the round-robin play with three wins from three.
"But of course I want to do well. I want to try to keep the momentum going and play the right way and, to do that, a win's always very helpful."
Federer will face the winner of Friday's clash between Dominic Thiem and David Goffin for a place in Sunday night's championship decider.
Saturday's other semi at London's O2 Arena will feature first-time Tour Finals combatants Jack Sock and Grigor Dimitrov.
Continuing his superb late-season run, Sock - the tournament's eighth and final qualifier - secured his spot in the last four with a spirited 6-4 1-6 6-4 win over world No.3 Alexander Zverev.
Earmarked as Federer's heir apparent, Zverev had promised to take care of Sock and join the Swiss great in the semi-finals.
Instead, he blew an early service break in the deciding set as Sock rallied to silence the German and advance to within a win of the biggest final of his career.
