KEY BISCAYNE, Fla. — Rafael Nadal fared badly on big points today, yet still won.

The Spaniard converted only four of 19 break-point chances but rallied to beat James Blake 3-6, 6-3, 6-1 in the quarterfinals of the Sony Ericsson Open.

Jelena Jankovic advanced to the women's semifinals when Elena Dementieva retired with a back injury trailing 6-3, 3-1.

Nadal's first service break came with a ferocious backhand passing shot for a 5-3 lead in the second set. He broke three more times in the final set, including on the final point. When a demoralized Blake hit his last forehand long, Nadal leaped and punched the air.

Ranked No. 2, Nadal is seeking his first tournament title this year and his first title at Key Biscayne. On Friday, he'll play the winner of Wednesday night's match between 10th-seeded Tomas Berdych and No. 31 Igor Andreev.

Andy Roddick will try to end his streak of 11 consecutive losses to Roger Federer when they meet in the quarterfinals Thursday.

Dementieva said her back began bothering her Tuesday, and she called it quits against Jankovic after 58 minutes.

The fourth -seeded Jankovic barely survived her opening match in the tournament. In the third set against Sofia Arvidsson, Jankovic overcame a 5-1 deficit, then saved five match points in a tiebreaker

"It was a scary feeling, you know, just thinking that I may be over with this tournament," Jankovic said. "But I was really strong mentally and was able to get through that match, which gave me a lot of confidence for the rest of the tournament."

The Serb has since swept every set in the past three matches.

Jankovic had never advanced beyond the third round in five previous appearances at Key Biscayne. She's seeking her first tournament title this year, and on Thursday she'll face the winner of Wednesday night's match between No. 13 Dinara Safina and No. 19 Vera Zvonareva.