Lopez won just one game before pulling out with an ankle injury
Top seed Rafael Nadal will take on Russia's Nikolay Davydenko in the final of the Shanghai Masters on Sunday.
World number two Nadal was 6-1 3-0 up in Saturday's second semi when fellow Spaniard Feliciano Lopez retired.
Sixth seed Davydenko had earlier beaten Novak Djokovic 4-6 6-4 7-6 (7-1) to end the Serb's hopes of adding Shanghai to last week's title in Beijing.
The result boosts Davydenko's chance of qualifying for the eight-man ATP World Tour Finals in London in November.
Davydenko, who is s currently ninth in the race to London, grew stronger throughout the match and held break points in the final set before taking the tie-break.
Djokovic edged the opening set with a break in game 10 but then smashed his racquet in anger - for the second day running - after missing a forehand pass on break point early in the second.
The 22-year-old was made to pay when Davydenko broke to go 4-3 ahead and went on to serve out the set.
It was the Russian who held the initiative at 3-3 in the final set but he could not convert his break-point chances, and it came down to a tie-break.
Davydenko dominated, winning a magnificent rally with an angled backhand for the early break and chasing down a cross-court backhand winner for 5-0 on his way to an impressive victory.
"I played a great match but he was too good, but I've had a great two weeks in China," said Djokovic.
The second semi-final was a far quicker affair, with Nadal taking the first set inside 30 minutes before Lopez had his right foot strapped by the trainer.
After dropping serve at the start of the second set, the 28-year-old called it a day to become the ninth withdrawal of the week.
"I was a little bit lucky yesterday," said Nadal, who made the semis when Ivan Ljubicic retired after two sets on Friday.
"Today I was winning but it's never nice to win like this, especially against a close friend like Feliciano.
"I just wish both players a speedy recovery. I'm just happy to be in the final - my first after the injury comeback."