As if the top eight tennis stars in the world weren't enough, Carlos Tevez pops in for a hit [GALLO/GETTY]
There was drama, confusion and a certain Carlos Tevez at the O2 Arena in London on Thursday night, as Group A drew to a close in the round robin stage of the ATP World Tour Finals.

After beating Roger Federer in three close sets, Juan Martin del Potro was left waiting for 15 minutes before he found out that he had reached the semi-finals of the end-of-season championships by just one game.

The ATP have since apologised for the delay, but there must have been very few people sure of the outcome.

Britain's Andy Murray had earlier struggled past a battling Fernando Verdasco in another epic encounter lasting the entire afternoon, and all to no avail.

A straight sets win would have sent the world number four through.

But by the time the Scot had finally won the match, it was as dark outside as it was inside the spectacular Thames-side setting.

And yes, it's very dark in there.

Fading Nadal

Around 17,000 people per session have graced the venue in London's south east, and they have all been treated to some flashes of tennis brilliance.

Sadly, the world's second best player, Rafael Nadal, has provided none of these.

The Spaniard has struggled throughout his three matches, losing them handily, each in straight sets.

The concern for many fans will be his alarming dip in form.

He has been renowned for the pace and trickery of his shots, but his undeniable talent was certainly not displayed.

Robin Soderling, the tournament's surprise package, blew the left-hander off the court, while Nikolay Davydenko and Novak Djokovic had easier wins than they anticipated.

Djokovic too, however, limped out of the tournament despite two wins out of three in Group B.

"It just goes to show the round robin is more dangerous than juggling with swords...one slip and you're gone!"

Chris Tortise

It just goes to show the round robin is more dangerous than juggling with swords...one slip and you're gone!

So, only one of the top four players in the world has made it through to the semi-final stage, with both matches being held on Saturday.

Neither Davydenko nor Soderling have ever won a match against the Swiss world number one, and it's the Russian who has the unlucky task of trying to down the crowd favourite Federer.

And Federer looked rusty against del Potro.

The Argentinean US Open Champion has warmed into the tournament after his early loss to home-favourite Murray, but may struggle against the in-form Soderling.

But will the underdogs of Group B cause upsets?

Probably not, but they will give all they've got.

Expect a Federer-del Potro rematch come Sunday, and if you have tickets, take some camping gear...it could be a long one.

Source: Al Jazeera