Torres shone in a one-sided contest that was effectively all over by the 11th minute after Chelsea had established a 2-0 lead with goals from Raul Meireles and Torres.
The Spanish striker, in the middle of a domestic suspension for his sending-off against Swansea City, added a superb second goal with a header after 27 minutes and he could have scored four times.
Torres might not be back to the lethal goal-shark he was at Liverpool, but he played an important role in Chelsea's biggest home win in the competition which equalled their best ever, 5-0 over Galatasaray in Turkey 12 years ago.
Victory was completed with further goals from Branislav Ivanovic and substitute Salomon Kalou and Genk were lucky to go home conceding only five.
SPENT FORCE
Chelsea will face far tougher sides than Genk this season, but on this performance Torres is far from the spent force some were predicting after the miserable start to his Chelsea career which had brought just three goals since his 50 million-pound move from Liverpool last January.
Chelsea boss Andre Villas-Boas praised the Spaniard.
"Fernando found scoring positions, but we like to promote collective performance as well as individual performance," he said.
"We are able to choose from the best. The choice fell to Fernando today and he performed very well."
Torres almost put his side ahead in the seventh minute but hit a post with only goalkeeper Laszlo Koteles to beat, but a minute later Chelsea took control when Meireles scored with a long-range shot.
They doubled their lead when Torres slotted home from a Frank Lampard pass three minutes later, and the Spaniard scored the best goal of the night with a glancing header after 27 minutes from a perfectly-placed Meireles cross.
Ivanovic then headed in a rare goal three minutes before the break from a Florent Malouda free-kick to make it 4-0 and at that stage it seemed as though Chelsea might equal Liverpool's all-time Champions League record 8-0 win over Besiktas in 2007.
However, Chelsea took their foot of the gas after half-time with Genk, missing three defenders and influential skipper David Hubert, offering little in the way of resistance.
Indeed the Belgian's most memorable contribution to the occasion was their vivid cerise kit which stopped them fading out of sight altogether.
"It is no shame to lose to Chelsea because they have too much quality and play at a different level from where we are," said Genk coach Mario Been.
"We were missing a lot of players so we weren't in the best shape."
Chelsea, who have now beaten four Belgian sides at the Bridge without conceding a goal, stayed top of Group E with seven points, one ahead of Bayer Leverkusen with Valencia on two and Genk on one.
