Second-seeded Rafa Nadal has not lost serve once in three one-sided victories at the US Open this week but he feels his service game needs improving in his quest for another title at Flushing Meadows.

Nadal might appear to be nitpicking given that his 6-4, 6-3, 6-3 battering of Ivan Dodig of Croatia on Saturday sent him into the fourth round and extended his 2013 hard-court record to 18-0.

But the 27-year-old Spaniard knows what it takes to win Grand Slams and the US Open in particular.