Andy Roddick said he is not surprised to see his rival Lleyton Hewitt causing a stir at Wimbledon again.

Hewitt, the 2002 champion, provided the biggest upset of the tournament so far when he beat fifth seed Juan Martin Del Potro 6-3 7-5 7-5 in the second round yesterday.

The Australian's record at Wimbledon is impressive, with a semi-final and two quarter-final appearances to go with his title triumph, while he has reached at least the fourth round for five successive years.

Hewitt, who along with Roger Federer is the only past champion in the men's draw - will be expected to beat Germany's Philipp Petzschner in the third round and could meet Roddick in the quarter-finals.

The sixth seed, who has lost six of his 11 meetings with Hewitt, said: "I don't think it's surprising (that Hewitt won).

"Lleyton's ball stays very low on the court. He's certainly capable of playing very well on this surface."

Roddick, twice a finalist at SW19, dropped a set for the second successive round, beating Russian Igor Kunitsyn 6-4 6-2 3-6 6-2.

Having struggled at times against both Kunitsyn and first-round opponent Jeremy Chardy, Roddick knows he will have to raise his level of performance against Jurgen Melzer in the third round.

Melzer knocked out German Benjamin Becker, for his second straight-sets win, and, although the Austrian has lost all of his eight previous career matches against Roddick, none have been played on grass.

"He's tough and super talented," added Roddick. "He likes coming forward and so it will be tough."

Eighth seed Gilles Simon recovered from a slow start to eliminate Brazilian Thiago Alves, the Frenchman winning 5-7 6-3 6-4 6-4 to set up a third-round clash with Romanian Victor Hanescu, who knocked out Nicolas Devilder.

Another Romanian, Victor Crivoi, was swept away by 12th seed Nikolay Davydenko, losing 6-4 6-4 6-2.

Spain's David Ferrer, seeded 16th, knocked out Fabio Fognini for the loss of only seven games, while Tomas Berdych also crushed Paul-Henri Mathieu in straight sets.

Fernando Gonzalez fought back from a set down to take his place in the next round, the 10th seed winning 6-7 (4-7) 6-4 6-4 6-4 against Argentinian Leonardo Mayer.

Former world number one Juan Carlos Ferrero ended the Wimbledon singles career of French veteran Fabrice Santoro.

The 36-year-old, who is set to retire at the end of the season, bowed out with a 6-7 (1-7) 6-3 6-4 6-3 loss as Ferrero set up a third-round meeting with Gonzalez.

Stanislas Wawrinka, the Swiss 19th seed, found life much easier on Court Three where he saw off Martin Vassallo Arguello of Argentina in straight sets.

Today sees the return of title favourite Federer to Centre Court.

The second seed takes on German 27th seed Philipp Kohlschreiber, who has lost in all three of their previous meetings.

There are likely to be plenty of aces on Court One when 6ft 10in Croatian Ivo Karlovic meets ninth seed Jo-Wilfried Tsonga, while fourth seed Novak Djokovic faces American Mardy Fish.