Melbourne:Russia's Marat Safin qualified for the Australian Open semi-finals here today when his South African opponent Wayne Ferreira retired with a stomach muscle injury at 5-2 in the first set. The 30-year-old Ferreira had made the quarter-finals of the Australian Open for the first time since 1992 after two titanic five set battles and after dropping serve in the third game he called the trainer to examine a stomach muscle strain. He struggled on for four more games before calling it a day. The ninth seeded Safin, who knocked out 13-times Grand Slam champion Pete Sampras in the fourth round, plays German seventh seed Tommy Haas in the semifinal. Haas beat former finalist Marcelo Rios of Chile 7-6 (7/2), 6-4, 6-7 (2/7), 7-6 (7/5) in the night match. Safin, who will turn 22 on Sunday's finals day, is the only Grand Slam champion left in a tournament which has lost seven of its top eight seeds. Haas, the world No 9, is the only top 10 player left in the championship. It is the second Grand Slam semi-final for the 23-year-old German, who played against eventual champion Yevgeny Kafelnikov in the last four here in 1999.