Andy Murray knows there is plenty of work still to be done if he is to qualify for the semi-finals of the Barclays ATP World Tour Finals for a second successive year.

The British number one began his Group A campaign in impressive fashion on Sunday with a 6-3 3-6 6-2 victory over US Open champion Juan Martin del Potro. But, with world number one Roger Federer and dangerous Spaniard Fernando Verdasco still to come in the round-robin stage of the event, Murray knows his perfect start could count for nothing.

"It obviously helps a lot," he said. "But you have got to pretty much win two matches out of the three to give yourself a chance. I could still win two and not go through. I'll try and get the next one out of the way. If I can win that one I'll put myself in a good position."

That will be a tough ask for the 22-year-old, with Federer waiting in the wings on Tuesday evening.

Last year Murray played one of his best matches to beat the 15-time grand slam champion in his final round-robin clash and prevent Federer reaching the last four. That effort took it out of him and he promptly lost his semi-final to Nikolay Davydenko, but ahead of the tournament Murray insisted his tactics were right.

There is no question of him taking it easy on Tuesday with victory likely to be enough to secure his passage out of the group, and the Scot believes the battling qualities he had to show against Del Potro will stand him in good stead.

After Murray raced into a 5-0 lead, the Argentinian suddenly found his form and the world number four spent much of the last two sets scrambling to retrieve his opponent's trademark ferocious groundstrokes.

The 22-year-old continued: "It's not just against him, against Roger or Rafa (Nadal) or Novak (Djokovic), all of them can go on streaks where they play great.

"It's like (Andy) Roddick, sometimes he serves unbelievable for a set and a half, then you get one chance. With him (Del Potro), he's got a big serve, long reach, goes for huge shots.

"You just have to try and find a way through that. Tactically, I've always been quite good. So I found a way through it. I was happy with a lot of parts of my game."