Andy Murray has admitted that his serve let him down during his defeat to Rafael Nadal at the ATP World Tour Finals at London's O2 Arena this afternoon.

The Spaniard dominated proceedings at the end-of-season event to move to the brink of the semi-finals, breaking Murray four times on his way to a 6-4 6-1 triumph.

Murray made just 43% of his first serves and won 34% of his points on second serve, and the Brit admitted that he did not do himself any favours against the former world number one.

"He obviously played better today than he did when I played him earlier in the year," Murray told reporters.

"Also I didn't help myself out there today. I served extremely low percentage, maybe lowest percentage I served the whole year in any match. That's not good enough against someone as good as Rafa."

Murray will face Stanislas Wawrinka in his final group game at the tournament.