Michalek scored the go-ahead goal midway in the second period, while Thornton got an assist on both of Cheechoo's goals, as well as on Michalek's third-period score. Thornton has 99 points this season (20 goals, 79 assists), vaulting him past Vincent Lecavalier of Tampa Bay (97 points) and into second place behind Sidney Crosby of Pittsburgh (108 points) in the NHL scoring race.
Patrick Sharpe notched his 17th goal for the Blackhawks, who were eliminated from playoff contention after the previous night's loss at Columbus. San Jose, meanwhile, remained right in the thick of the Western Conference race, moving past Minnesota (93 points) and into fifth place with 94 points.
Sharks goalie Evgeni Nabokov stopped 28 shots as San Jose swept the season series from Chicago, 4-0.
The game was even through the first period and a half. Cheechoo opened the scoring in the first period when Thornton skated around the Blackhawks' defence and found Scott Hannan at the point. Hannan faked a shot and fed Cheechoo, who was alone at the side of the goalmouth.
Sharpe answered for the Blackhawks with just under five minutes left in the first period, converting a point-blank shot past Nabokov, who had just made a save on Chicago's Rene Bourque. Nabokov came up with more big saves in the second period, which included a diving stop on Martin Havlat. Nabokov also had a bit of luck when Brent Seabrook's shot from the point caromed off the inside of the goalpost and went underneath Nabokov, but not into the net.
The game remained close until San Jose cranked up its power play, which is ranked second in the league.
The Sharks converted on two of their five man advantages. Michalek scored the go-ahead goal on assists by Matthew Carle and Craig Rivet. Carle fed the puck right across the crease and Michalek was there to tip it past goaltender Patrick Lalime.
San Jose's power play struck again early in final period. Thornton's cross-ice feed deflected off Carle and went to Michalek, who buried the shot.
San Jose's three scoring stars on the night teamed for the final goal. Cheechoo began the play with a pass behind the Blackhawks net to Thornton, who found a wide-open Michalek in the slot.
Notes: With their elimination Tuesday night from the Western Conference playoffs, the Blackhawks have not made a post-season appearance since 2002. ... Before Wednesday's final meeting, San Jose had outscored the Blackhawks 13-3 in their three victories. ... The Sharks are second in the NHL in power-play conversion (22 per cent), while the Blackhawks are last (12.4 per cent).