Fuhr strained a ligament in his right knee while stretching to stop a shot. He came out of the game with 7:29 left in the second period, having allowed three goals on 17 shots.
The extent of Fuhr's injury was not immediately clear.
Mike Ricci and Stephane Matteau added goals for the Sharks, who broke a two-game losing streak. San Jose, which moved ahead of idle Edmonton into eighth place in the Western Conference, is 18-0-2 this season when leading after the second period.
Geoff Courtnall scored his 23rd goal for St. Louis, which is 0-18-3 this year when trailing after the second period.
Joel Quenneville coached his 100th NHL game for the Blues. He has a 48-37-15 record for St. Louis. Red Berenson and Mike Keenan are the only Blues coaches with more wins than Quenneville in their first 100 games.
Friesen opened the scoring just 67 seconds into the game on a power play. Blues defenseman Marc Bergevin was called for interference only 10 seconds into the game, the first for both teams since NHL referees have been instructed to be tighter in calling penalties.
Courtnall tied the game less than 4½ minutes later, but the Sharks scored twice in the second period to take control. Ricci scored with 4:48 gone in the period on a rebound, and Matteau scored on a deflection less than a minute later.
The Sharks did not get a shot on goal in the third period, but St. Louis never threatened seriously in the final period.
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