Halep, junior champion at Roland Garros in 2008, will face Andrea Petkovic tomorrow for a place in the final on Saturday after the German beat the Italian Sara Errani, runner-up in Paris two years ago, by the same 6-2, 6-2 scoreline.
Kuznetsova, the No.27 seed who won the title in 2009 to go with her 2004 US Open title, took a medical timeout after the first set and came back with her left thigh strapped. She wasted break points early in the second set and made numerous forehand errors as Halep wrapped it up on the first match point when Kuznetsova netted a service return. The Romanian converted six of her eight break points while Kuznetsova missed seven of her nine.
"I strained a muscle during the [last-16] match against [Lucie] Safarova, and then I was struggling with the pain," said Kuznetsova. "I managed to do it without a medical timeout in the Safarova match, but today it got worse."
Not a hard hitter, Halep compensates for her relative lack of power with her tactical nous. Prowling along the baseline, she moved Kuznetsova around with crosscourt shots, forcing the Russian to misfire. "It was a perfect day for me," said Halep. "I played really well. I was very aggressive. I played very fast."
Petkovic also reached the semi-finals of a grand slam for the first time. The No.28 seed was quicker to hit her stride in chilly, gusty conditions and, despite losing her first service game, was always the more aggressive player. She is playing at the French Open for the first time since 2011 when she reached the last eight.