World number one Andre Agassi rates Wednesday's big-hitting shootout between bookies' favourite Andy Roddick and British number two Greg Rusedski as a highlight that is too close to call.

The pair jointly hold the record for the fastest recorded serve at 149 mph (240 kph), have met twice before with honours even and are both looking in fine grasscourt fettle.

"That's certainly going to be an interesting match to say the least ... I really believe it's 50-50," Agassi said after his first-round win on Tuesday. "It's going to be an enjoyable match to watch.

Roddick beat Rusedski at Queen's Club 10-days before Wimbledon, but the Briton went on to win the Nottingham tournament last weekend, so both have tasted grasscourt success this year.

The duo's previous meeting was at Wimbledon last year when Rusedski beat Roddick in straight sets in the fourth round.

Seeded five, Roddick is quoted as the 11-4 favourite for the title, playing in the side of the draw that lost top seed Lleyton Hewitt on Monday.

Fourth seed Roger Federer meets left-hander Stefan Koubek of Austria in what could also be an awkward match for the talented Swiss who has yet to produce his best tennis in Grand Slams.

Women's fourth seed Venus Williams, who follows Federer on to Centre Court should have no such problems against Slovenia's Katarina Srebotnik, ranked 42 in the world.

The twice former champion teams up with defending singles champion Serena later so the sisters can begin the defence of their doubles title.