PARIS—Dusan Lajovic of Serbia will make his debut in the fourth round of a Grand Slam tournament after beating Jack Sock of the United States 6-4, 7-5, 6-3 Saturday at the French Open.
The 83rd-ranked Lajovic is playing in only his second major tournament. He lost in the second round at the Australian Open in January.
Lajovic saved 8 of 9 break points he faced against the 75th-ranked Sock, who was born in Nebraska and was trying to join John Isner as the first American men in the fourth round at Roland Garros since 2010.
Sock, 21, has yet to reach the final 16 at a major.
Before this French Open, the 23-year-old Lajovic had a 10-21 career record in tour-level matches, never winning two in a row.