Roger Federer is just one win away from becoming the ATP World Tour Finals champion for a seventh time, but to do so he must face Novak Djokovic - himself looking for a third consecutive title - after overcoming Stan Wawrinka 4-6 7-5 7-6 in an unbelievably epic semi-final contest inside the O2 Arena.
If the Tour Finals have been lacking in quality this week until now, these two Swiss stars more than made up for it in what was the longest singles match - nearly three hours - of the entire competition.
In a match of twists, turns, ups and downs - Wawrinka blew a couple of match points in the deciding set, Federer struggled to make the most of his various reprieves, while both produced some amazing moments of magic to fully justify their last four billing.
Eventually it was Federer who held his nerve in a nail-biting tie-breaker in the third and final set to set up a dream clash with Djokovic, the world no.1, in the London and season finale.
The Swiss no.1 was delighted to scrape through when he spoke on-court: "I think I got lucky tonight. Stan played better from the baseline and that usually does the job on this court. But I kept fighting. It's tough but I'm thrilled to be in another final in London.
"Novak is playing great tennis. It usually brings the best out of me, it's going to be tough but I'll give it a shot."
It is perhaps fitting that it should be two of tennis' most successful ever players will meet for the 37th time in their careers. Between them they hold an amazing 24 Grand Slam titles and nine World Tour Finals titles.
STAN THE UNLUCKY MAN
Wawrinka's performance cannot be underestimated, however, and thoughts must go out to the world no.4 after he lost four match points and trudged off the court looking utterly dejected.
It was the Swiss no.2 who started the better as well. The 29-year-old's ferocious serve was proving too hot to handle for his compatriot and he combined that hitting power with stringent defence against the 17-time Grand Slam as he took a set lead.
At 33-years-old you could have forgiven Federer for giving into the inevitable moans and groans from his aging and weary legs, but instead he showed exactly why he has had won so many accolades over the course of his career.
The second set went with serve right up until 6-5 when the former world no.1 broke Wawrinka to set up a decider.
Federer was then down a break early in the third and struggled to get on terms with his hyped-up opponent. As a result Wawrinka was serving for the match at 5-4 and dropped three match points before being broken.
At 5-5 both struggled on their serves and dug themselves out of holes, but they did pull through the tie-break.
The tie-break was just as topsy turvy. Federer lost a 2-0 and 4-2 lead and Wawrinka had another match point when he came from behind to make it 6-5. However, in one last show of grit and quality, Federer saved the fourth match point and then rattled through three consecutive points to ensure his Djokovic final.
Indeed the Serb will have been delighted with what he witnessed from the comfort of his bed as the two potential finalists push their body to the limits less than 24 hours before the final.
Earlier in the day he had things slightly easier against Kei Nishikori in a 6-1 3-6 6-0 triumph.
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