Following the previous day's upsets, Halep restored a sense of order with a 7-6(5), 6-2 win on Philippe Chatrier. However, it was far from straightforward for the No.6 seed and 2014 finalist, who surrendered serve twice to trail 4-1 in the first set.
The procession of breaks continued into the second, before the Romanian gained control of proceedings, wrapping up victory when Diyas flicked a forehand long to end another extended baseline exchange.
"I expected a tough match. I played two times against her and I know that the score was easier, but still I felt she was very dangerous," Halep said.
"She has a flat game and today she played really well. First set she was hitting all the balls and very flat, so the ball didn't bounce too much. I stayed a little bit too far from court. But in the end I found the rhythm. I found the way to play aggressive, to dominate the game, and I finished it in two sets."
The only other time Halep made it through to the third round in Paris was in 2014 when she ended up going all the way to the final. Her next challenge comes in the shape of Naomi Osaka after she eased past Mirjana Lucic-Baroni, 6-3, 6-3.
"I'm not thinking about finals. It's very far. I'm thinking just for the third round," Halep said. "I had two good matches here already. I'm looking forward to play the third one. I expect a tough one. She's a young player and she has nothing to lose. It's going to be good match, and hopefully I will win it. I'm here to win."