The Australia international finished from close range after a delicate chip into the box by Landon Donovan, although the ball fell to Cahill after what looked like a handball by Marouane Fellaini.
Blackburn levelled when Tim Howard failed to deal with a high ball into the box and David Goodwillie
- in the side in place of the suspended Ayegbeni Yakubu - charged down
Cahill's attempted clearance to force the ball home in the 72nd minute.
In the late kick-off, Bolton Wanderers secured only its second home win of
the season with a 3-1 victory over Liverpool that lifted it out of the
Midfielders Mark Davies and Nigel Reo-Coker gave the home side a
deserved 2-0 lead inside half-an-hour before Craig Bellamy reduced the
deficit in the 37th minute.
However, five minutes into the second half Gretar Steinsson restored
the two-goal cushion as the Trotters dealt a blow to the Reds' hopes of
closing in on the top four.
Newcastle United missed a chance to rein in fourth-placed Chelsea as it succumbed to a 5-2 defeat to Fulham at Craven Cottage.
The Magpies led 1-0 through Danny Guthrie's 43rd-minute effort and looked set to cut the Blues' lead over them to two points, but Fulham fought back superbly in the second half to secure only its second win in six league games.
Danny Murphy equalised from the spot in the 52nd minute after Davide Santon fouled Damien Duff and Clint Dempsey steered in a rebound after Newcastle goalkeeper Tim Krul parried a Bobby Zamora shot to make it 2-1 seven minutes later.
The American scored his second in the 65th minute before Zamora converted Fulham's second penalty, conceded by Krul for a foul on Andrew Johnson. Hatem Ben Arfa cut the gap to two but Dempsey completed his hat-trick in the 89th minute from a Zamora pass.
Earlier, Fernando Torres and Chelsea were left frustrated as the fourth-placed Blues were held to a goalless draw at mid-table Norwich City in the lunchtime kick-off.
Canaries goalkeeper John Ruddy kept Torres out in the first half and Juan Mata in the second as Paul Lambert's side kept its first clean sheet of the season and denied Andre Villas-Boas' side a fourth straight win.
Queens Park Rangers climbed out of the bottom three with a 3-1 win over bottom club Wigan Athletic at Loftus Road in Mark Hughes' first home league game in charge.
Heidar Helguson opened the scoring with a 33rd-minute penalty after James McCarthy handled the ball in the box before Akos Buzsaky added a second with a stunning free-kick which flew in off the post.
Hugo Rodallega's curling effort halved the deficit (66) and Helguson's penalty was then saved by Ali Al Habsi to keep the Latics in contention, but Tommy Smith's stunning right-foot strike from long range sealed the victory for QPR, which had taken just one point from its previous seven league games.
QPR's win dropped Wolverhampton Wanderers into the bottom three, as it lost 3-2 at home to Aston Villa, for whom former Molineux favourite Robbie Keane scored a brace.
Darren Bent gave the visitor the lead in the 11th minute after he nicked the ball off Christophe Berra and was tripped in the box.
Michael Kightly levelled after 20 minutes when he shaped to cross from the right, cut inside and angled a left-foot shot across Shay Given into the far corner and Dave Edwards' close-range header after half-an-hour put Mick McCarthy's men ahead at the break.
Keane, on loan at Villa from Los Angeles Galaxy, levelled after 50 minutes and then drilled in a superb second in the 84th minute from the edge of the box. Karl Henry's red card for a petulant swipe at Marc Albrighton completed a miserable day for McCarthy's side, which extended its winless league run to eight games.
Sunderland's revival under Martin O'Neill continued as it won 2-0 at home to Swansea City. It claimed its fifth win in eight league games under the Northern Irishman as Stephane Sessegnon scored the first with a wonderful angled shot after a one-two with James McClean in the 14th minute and then set up Craig Gardner to fire in a spectacular strike (85).
West Bromwich Albion ended a run of three straight league defeats with a last-gasp 2-1 win at Stoke City.
James Morrison gave the Baggies the lead with a swerving shot 10 minutes before the break which deceived Thomas Sorensen. Cameron Jerome equalised for Stoke but Graham Dorrans' free-kick in injury-time evaded everyone and found the corner of the net.