HE'S here all week.

The customary compliment to a successful comedian last night was applied to Andy Murray after the Scot returned to the O2 Arena for an encore after a midweek performance that had been, well, disappointing. Murray was beaten 6-0, 6-1 by Roger Federer on Thursday to go out of the Barclays ATP World Tour Finals but was called up at home in Oxshott in Surrey yesterday afternoon to come to the rescue of a tournament that was suddenly roaring: "One of our finalists is missing!"

Federer had injured his back in an epic semi-final victory over Stanislas Wawrinka on Saturday night and Murray was drafted in for an exhibition match against tour champion and world No.1 Novak Djokovic.

"I have to apologise because clearly I pushed Roger so hard on Thursday," Murray, channelling his inner Chic Murray, told the crowd of 17,000 who had been earlier told on court by Federer that the Swiss could not play.

Plan B involved Chris Kermode, the executive chairman and president of the ATP, calling Murray and the Wimbledon champion driving in to play an exhibition set against Djokovic and a set of doubles, in partnership with John McEnroe, against Tim Henman and Pat Cash. Murray - and the others - received not a penny in recompense though Djokovic was consoled for missing out on a final match with a winner's cheque for $2,075,000. The 17,000 crowd, who paid up to £120 for a ticket, will be offered a partial refund, still to be decided.

It was only the third time Federer had pulled out of a tournament in progress. He left Bercy in 2008 and Doha in 2012 also because of back problems. He has never withdrawn during a match despite playing 1221 of them.

Last night's drama was precipitated by Federer suffering an injury during his dramatic victory over Wawrinka. "This back spasm, whatever it might be, it's just not a fun thing to have during the day. It's just uncomfortable. But I'm positive and I'm hopeful that it's going to go away very soon," he said yesterday afternoon.

Federer is scheduled to play this week in the Davis Cup final against France. The situation for Switzerland is further complicated by reports last night that compatriots Wawrinka and Federer had fallen out over comments made during the semi-final. Wawrinka, too, had apparently complained about comments coming from Federer's team.

This controversy existed in whisper and claim last night but what was certain was that at one point the ATP was left with one final, 17,000 spectators, a worldwide television audience and no-one to play Djokovic. Kermode, waiting for confirmation that Federer could not take part, initiated Plan B, alerting Murray to the possibility he may have to save the day.

The Scot immediately drove from Surrey to North Greenwich, arriving at 5pm. He then played Djokovic shortly after 6pm, losing a superset 8-5 in 47 minutes before taking part in the doubles match, which he and McEnroe won, despite the Scot playing against Supermac, Henman and Cash at one point.

"I want to thank him for coming out and making an effort," said Djokovic. "It really is an effort. I know how it feels when you finish the season, as he did on Thursday. Probably the last thing he's thinking about is tennis now. He wants to rest after a long season. He receives a call. He comes out and plays an hour. Now he's still playing doubles."

The world No.1 added: "It's very genuine from him. I tried also to play. I thought we played on a good level. I hope the crowd enjoyed it because there was not much you can do really."

The Serb admitted that the presentation of the trophy had left him feeling "awkward" and the withdrawal of Federer was the final blow for a competition that must have valid claims for the unwanted title of Worst Tennis Tournament Ever. There was only one match of consequence and drama - the semi-final between Federer and Wawrinka - and that ironically came with a sting that would have been worthy of a scorpion with a septic tail.

Federer finished his press conference after that titanic, three-set match at 1am. This left him 17 hours to have a massage, stretch, rehydrate, eat, sleep and practice before facing the best player in the world. This schedule alone would have been enough to test his 33-year-old frame without the added complication of the back injury.

His withdrawal ensured the tournament ended with two hours of entertainment rather than a full-blooded contest between world No.1 and world No.2.

There was, though, a bonus for Murray. There had been speculation that he would be booed this week by a crowd in London because of his pro-independence stance. Instead, he was cheered all week and even brought laughs to an arena deprived of a competitive final.

The crowd will receive a partial refund but Murray was rewarded in the currency of ending his season with a victory in the shape of that doubles triumph with McEnroe.

And he left the O2 at the end of finals day with a smile. It is hoped that in 2015 Murray, comedian and competitor, will be here all week.