Toby Flood produced an immaculate display with the boot as Leicester edged out Bath at a soggy Welford Road.
A Flood drop-goal and three penalties sent the Tigers in 12-6 ahead at the break as Bath's Olly Barkley could only make two of his four kicks.
With running rugby impossible after heavy rain, two more Flood penalties seemed to put the Tigers in charge.
Three Barkley penalties set up a nervy finish but Flood's sixth penalty out of six sealed it.
The victory ensured the Tigers got their title defence back on track after an up and down start to the season, while although Bath left with a losing bonus point, they have now lost four of their last six games in all competitions.
Bath had not won at Leicester since November 2003 and, without injured England captain Lewis Moody, they got off to a dreadful start as Sam Vesty kicked directly into touch from outside his own 22, and from the resulting scrum Flood picked up Ben Youngs' pass off his toes to drop a goal.
A sixth-minute Flood penalty doubled the Tigers' lead, before Barkley kicked one of his own as the visitors finally got out of their own half.
Two further Flood penalties gave Leicester a nine-point lead as Bath's ill-discipline cost them dear, but Barkley had his side back in the game with a brilliant penalty from half-way.
But two missed chances before the break proved crucial as Flood kept slotting his kicks between the posts when Bath infringed to make it 18-6 early in the second half.
Barkley finally found his radar to pull his side back into the game with three unanswered penalties.
But after a powerful Tom Croft surge gave the home side field position, Flood's sixth penalty eight minutes from time effectively won the contest as Bath's late attacking surge came to nothing.
Leicester director of rugby Richard Cockerill: "It was pretty ordinary for both sides. When that downpour came it ended the game as a spectacle.
"It was a bit frustrating as it becomes a lottery and you don't get the true result as you don't know how the sides would have played in good weather. It ends up being a game of errors and penalties.
"We should have controlled the game at 12 points up and we need to work on that. They should not have been playing for the game near the end but I didn't think they looked like scoring a try."
Bath coach Steve Meehan: "I was very pleased with the effort we showed and the way we stuck to our guns.
"The pack did very well and our inside backs kicked intelligently which was what was required. A couple of calls go for us instead of against us and it could have been different.
"That was our best wet-weather performance in years. If we play like that every week we are going to win more than we lose. We were prepared to stick to our plans and not go off-piste. For the players to apply themselves and go against their natural grain is a sign of maturity."
Replacements: McMillan for Claassens (68), Catt for Flatman (67), Skirving for C. Fernandez Lobbe (73). Not Used: Batty, Wilson, Van der Glessen, Biggs, Cuthbert.
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