LONDON (AFP) - Sloane Stephens became Wimbledon's first big-name casualty this year as the world No. 4 crashed to a shock 6-1, 6-3 defeat by Croatia's Donna Vekic on Monday (July 2).

Stephens had been expected to mount a strong challenge at the All England Club after winning her maiden Grand Slam crown at last year's US Open and finishing as French Open runner-up last month.

But the 25-year-old American, who has been in fine form since returning from foot surgery last year, had only gone past the Wimbledon third round once in six previous visits.

She was beaten in the first round last year and maintained her poor record on grass with another limp display against world No. 55 Vekic on Court 1.

Vekic, who sealed the upset on her fourth match point, faces Slovakia's Viktoria Kuzmova or Sweden's Rebecca Peterson in the second round.

In the men's draw, Roger Federer started his 20th straight Wimbledon campaign by cruising to a 6-1, 6-3, 6-4 win over Serbia's Dusan Lajovic.