Riske broke Halep’s serve three times in the first set, but the Romanian found her rhythm to wrap up victory on Court Philippe Chatrier.
Fourth seed Elina Svitolina advanced with a regulation 6-3 6-4 victory over Slovakia’s Viktoria Kuzmova while twice Wimbledon champion Petra Kvitova took just over an hour to beat Spain’s Lara Arruabarrena 6-0 6-4.
Second seed Caroline Wozniacki turned in a ruthless display to defeat big-serving Spanish qualifier Georgina Garcia Perez 6-1 6-0 in 51 minutes.
In the men’s draw, former champion Novak Djokovic was far less clinical, letting loose a number of wayward shots, but still had too much class for Spanish qualifier Jaume Munar in a 7-6(1) 6-4 6-4 win.
Djokovic will next face claycourt specialist Roberto Bautista-Agut, who beat Colombia’s Santiago Giraldo 6-4 7-5 6-3.
Alexander Zverev and Grigor Dimitrov were both stretched to five sets in their second-round victories.
Zverev, seeded second, beat world number 60 Dusan Lajovic 2-6 7-5 4-6 6-1 6-2 to claim his 32nd win of the season.
Fourth seed Dimitrov battled past American Jared Donaldson 6-7(2) 6-4 4-6 6-4 10-8 to match his best performance at Roland Garros by reaching the third round for the third time.
