World number one Roger Federer overcame rain and the tallest man in tennis to belatedly claim his place in the quarter-finals of the Swiss Open on Friday.

Wimbledon champion and commanding leader in this year's rankings, the Swiss top seed beat Croatian Ivo Karlovic 6-7, 6-3, 7-6 in a delayed second round clash.

The match had been due to be played on Thursday afternoon, but was postponed because of cloudbursts at the Swiss Alpine resort where Federer, 22, is seeking to win his home event for the first time.

Federer, meeting the 6ft 10ins (2.083 metre) Croatian for the second time in 11 days following his fourth round triumph at Wimbledon, struggled to find his best form on the clay court of the Roy Emerson Arena.

"I have played six sets against him now and four of them have gone to a tiebreak," he said. "That shows how difficult it is to play against his service. I had to work hard to win this game."

Asked to compare the service of Karlovic with that of defeated Wimbledon finalist American Andy Roddick, who holds the record for the fastest, Federer said: "They are both very fast, but I think that Karlovic's second serve is a little stronger."

UNFINISHED MATCH

Federer, who lost to Czech Jiri Novak in last year's final, is due to meet his Swiss Davis Cup captain Marc Rosset or Czech Radek Stepanek in the last eight later on Friday.

Their unfinished match from Thursday was due to continue following Federer's victory with Rosset one set ahead before thunderstorms prevailed.

In front of a sell-out capacity 5,800 crowd, ringing bells to urge on their hero, Federer extended his successful streak to 22 wins in 23 matches, but did not find it easy against fast serves that flew off the court in the relatively thin air at an altitude of more than 1,200 metres.

His own service and considerable artistry with ground strokes that often left Karlovic flat-footed were enough to carry him through, however, and keep alive his dream of taking the Swiss title for the first time in seven attempts.