Nicolas Anelka's second-half strike was enough for Bolton to battle past bottom side Watford at Vicarage Road.
Bolton's Nolan congratulates Anelka for his goal
Hornets keeper Ben Foster fumbled Gary Speed's 64th-minute corner and Frenchman Anelka fired home for his ninth goal of the season.
The visitors had dominated the first-half exchanges with Anelka denied by a brilliant Foster parry.
Watford started strongly after the break but once Anelka netted, the visitors always looked comfortable.
Bolton had started well with Anelka's rasping third-minute free-kick setting the tone for an opening 20 minutes of near-total domination.
The Hornets finally carved out two good opportunities during a lively 10-minute spell mid-way through the half when Jay DeMerit headed Lee Williamson's free-kick over the bar.
606 DEBATE: Your reaction to Bolton's victory
Then Jordan Stewart's sweet 15-yard strike was blocked by Bolton's Tal Ben Haim.
Foster was again called upon to keep his side in the game when he brilliantly turned away Anelka's powerful left-footed drive after 40 minutes.
And the hosts had good reason to claim for a penalty on 43 minutes when Darius Henderson's shot seemingly bounced off Bolton defender Abdoulaye Faye's arm, but was cleared to safety.
Williamson had Watford's best chance just before the break but Faye again did well to slide across the area and block the effort with his legs.
Watford were quickly out of the blocks after the break and an incisive move down the right freed up Adrian Mariappa, whose side-footed shot ripped past Jussi Jaaskelainen's far post.
Foster denied substitute Andranik Teymourian, on for the injured Stelios Giannakopoulos, after the break with another fine save in the 57th minute.
But the on-loan Manchester United stopper was unlucky to have his fine performance marred by one telling mistake.
Anelka's winner - his eighth in the Premiership - sealed the Trotters' first top-flight since Christmas.
But there was late controversy when Bolton keeper Jussi Jaaskelainen was only booked for coming out from his area to block a Watford through ball with his hands but Gareth Williams' free-kick was cleared to safety.
Watford manager Adrian Boothroyd:
"It was not a good performance, let's not gloss over anything. It was a bad game and we contributed to that enormously.
"We had an opportunity to get something today because, as good as Bolton are, they didn't play play particularly well but we never turned up today.
"I expected us to get points but we didn't turn up. We have got ourselves in a hole and we have got to get out of it. But if we carry on playing like that we will only make it deeper."
Bolton boss Sam Allardyce on Nicolas Anelka:
"You always need a bit of quality at the right time at this level and there wasn't a lot of quality out there until Anelka popped up and put it in the back of the net.
"That's why you pay so much money for that sort of talent. It's about sticking the ball in the back of the net if you get the chance.
"He has been a massive added bonus to our squad this year and hopefully he can carry on like that to the end of the season."
Watford: Foster, Mariappa, DeMerit, Mackay, Stewart, Williamson (Williams 46), Mahon, Francis (Kabba 77), Bouazza (McNamee 68), Henderson, Hoskins. Subs Not Used: Lee, Doyley.
Bolton: Jaaskelainen, Hunt, Meite, Faye, Ben Haim, Nolan, Campo, Speed, Diouf (Pedersen 80), Anelka, Giannakopoulos (Teymourian 50). Subs Not Used: Walker, Gardner, Tal.
Booked: Faye, Teymourian, Jaaskelainen.
Goals: Anelka 63.
Ref: R Styles (Hampshire).