US Open - Serena crushes Pennetta to reach semi-finals

The two-time defending champion, who is looking for her first grand slam title of the year, found herself 3-0 down in a matter of minutes but was hugely impressive thereafter in a 6-3 6-2 victory.

Williams has not lost more than three games in any set yet this tournament and will be a big favourite to beat surprise semi-finalist Ekaterina Makarova.

She said: "I felt she was playing really well, I don't feel I was doing too much wrong (in the first three games).

"I just said to myself that if she keeps it up then she absolutely deserves the win and I just tried to do a little better. I had a lot of fun today, I really enjoyed it and I'm so happy to have won."

Williams was the only top-eight seed to have made the last eight, with 10th seed Caroline Wozniacki the next highest.

"I've had a tough year in the majors," said Williams. "I've gone down to some great players outside of the top 10 so you can never underestimate anyone. We're all fighting really hard and we all deserve to be here."

Williams had cut a calm and focused figure throughout the first four rounds, with none of the nervousness that led to early defeats in the other three slams.

But Pennetta, who made the semi-finals here last year, came out with a very aggressive approach and broke the fearsome Williams serve twice in succession.

The world number one ensured that was as big as the gap got, though, and reeled off the next three games, letting out several screams of, 'Come on'.

Pennetta had never beaten Williams in five previous meetings and it seemed normal service had been resumed when she made it five games in a row.

Successive double faults from Williams gave Pennetta the chance to get back into the set but the opening was snatched away as quickly as it arrived.

Williams looked like a woman on a mission as she thumped groundstrokes but Pennetta did manage to stop the consecutive run of games against her at six by holding serve to start the second set.

There was nothing the Italian could do in the fifth game, though, as a barrage of Williams power earned her a break to love.

The American was on a roll and a run of five straight games wrapped up the win in just an hour and three minutes.