WIMBLEDON --Top-seeded Pete Sampras, yet to lose a set in four matches, powered into the Wimbledon quarterfinals Monday, and Todd Martin thwarted a comeback bid by former champion Andre Agassi. Michael Chang routed French Open champion Sergi Bruguera in a battle of baseliners, and four American women, led by Martina Navratilova, also charged into the quarterfinals. Navratilova, in her farewell Wimbledon at age 37, crushed Helena Sukova, 6-1, 6-2, slamming an ace on match point to move a step closer to her 10th title. Sampras handled Daniel Vacek of the Czech Republic, 6-4, 6-1, 7-6 (7-5) in only 87 minutes. Asked if he was a notch above the rest of the competition, Sampras said: "I feel whenever I step out on the court, if I play my tennis, I'm very tough to beat."Martin, the No. 6 seed, reached the quarterfinals for the second straight year with a 6-3, 7-5, 6-7 (7-0), 4-6, 6-1 victory over Agassi, which included 22 aces. Agassi, who won Wimbledon in 1992, had the crowd on its feet as he took the fourth set, but Martin bore down in the fifth, winning the last game to love. "He really raised his level of play," Agassi said of the last set. "He started taking big chances and it just seemed like it was working for him. I didn't really have an answer for him." Fourth-seeded Goran Ivanisevic, another big server, lost his first set in four matches, but beat Alexander Volkov of Russia, 7-6 (7-3), 7-6 (8-6), 4-6, 6-2. Chang, a former French Open champion seeded 10th, dominated the eighth-seeded Bruguera, 6-4, 7-6 (9-7), 6-0 to get past the fourth round for the first time in seven Wimbledons. Chang will play Sampras in the quarterfinals, and Martin will play unseeded Wayne Ferriera of South Africa, who beat Jonas Bjorkman of Sweden, 6-3, 6-7 (7-2), 6-4, 6-3. American Bryan Shelton lost to Sweden's Christian Bergstrom, 3-6, 6-3, 3-6, 6-3, 10-8. Lori McNeil outlasted Florencia Labat of Argentina, 7-6 (7-4), 7-6 (7-4) to make the quarterfinals. Two other American women reached the quarterfinals for the first time. Lindsay Davenport, seeded 9, routed Gab-riela Sabatini, 6-1, 6-3, and veteran Gigi Fernandez, in her 10th try here, beat Yayuk Basuki of Indonesia, 6-4, 6-1. In later men's matches, three-time champion Boris Becker faced No. 9 seed Andrei Medvedev and France's Guy Forget faced Jeremy Bates, seeking to become the first British man in the quarterfinals since 1973. Among the women, third-seeded Conchita Martinez beat Kristine Radford of Australia, 3-6, 6-3, 6-4, and fifth-seeded Jana Novota advanced with a 6-3, 6-3 win over Naoko Sawamatsu of Japan. Novota next plays Navratilova, and Martinez plays Davenport. Larisa Neiland, playing in her 11th Wimbledon, joined Davenport and Fernandez as a first-time quarterfinalist. The Latvian rallied past Amanda Coetzer of South Africa, 1-6, 6-3, 6-4 and will play McNeil in the quarterfinals.