Luke Berry netted inside the first minute as Cambridge moved to the top of the Conference Premier after victory against Forest Green.
A mistake from keeper Sam Russell allowed the midfielder to sweep the ball into an unguarded goal after just 56 seconds.
Richard Tait hit the crossbar before Tom Champion headed the U's second.
Rovers replied when Yan Klukowski pounced on keeper Chris Maxwell's error to tap in but it was not enough.
VIEWS FROM THE DRESSING ROOM
Forest Green Rovers manager Dave Hockaday told BBC Radio Gloucestershire:
"It's two individual errors that's given them the win and that's disappointing, but you can't do a great deal about individual errors.
"We had a go and left ourselves wide open at the end because we just wanted to go and get something from the game and on another day we would have got it.
"It's disappointing and we shouldn't be losing two games on the bounce, and we were certainly good enough to get something today.
"We've got to recover, you're only as good as your last game. We've got to get ourselves mentally and physically right for Tamworth on Tuesday."
Live Text Commentary
Full Time The referee brings the game to a close.90:00 +5:11
Al Bangura takes a shot. Blocked by Greg Taylor.90:00 +4:28
Shot by Liam Hughes went wide right of the target.90:00 +3:06
Adam Cunnington receives a caution for unsporting behaviour.90:00 +3:06 Booking
Free kick awarded for a foul by Harrison Dunk on Jamie Turley. Sam Russell takes the free kick.90:00 +0:24
Luke Berry takes a shot. Sam Russell safely holds on.89:00
Short corner worked by Anthony Barry.87:54
Unfair challenge on Magno Vieira by Greg Taylor results in a free kick. Chris Stokes crosses the ball in from the free kick.86:49
Matthew Barnes-Homer challenges Josh Coulson unfairly and gives away a free kick. Josh Coulson takes the free kick.86:04
James Norwood is flagged offside by the assistant referee. Free kick taken by Chris Maxwell.84:22
Nathan Arnold takes a shot. Jamie Turley gets a block in.83:22
Harrison Dunk takes a shot. Sam Russell safely holds on.82:05 Booking
Chris Stokes gives away a free kick for an unfair challenge on Adam Cunnington. Chris Stokes shown a yellow card. Richard Tait takes the free kick.79:50
Foul by Adam Cunnington on Eddie Oshodi, free kick awarded. Sam Russell restarts play with the free kick.78:03 Booking
Free kick awarded for a foul by James Norwood on Richard Tait. James Norwood is shown a yellow card. Chris Maxwell takes the free kick.77:06
James Norwood takes a shot. Matthew Barnes-Homer gets a block in.73:04
Nathan Arnold crosses the ball in from the free kick.
Substitution Liam Hughes replaces Ryan Donaldson.73:04
Free kick awarded for a foul by Al Bangura on Tom Champion.72:14
Free kick awarded for a foul by Chris Stokes on Nathan Arnold. Free kick crossed by Ryan Donaldson restarts the game.70:20 Booking
Foul by Matthew Barnes-Homer on Chris Maxwell, free kick awarded. The referee cautions Matthew Barnes-Homer for unsporting behaviour. Chris Maxwell restarts play with the free kick.69:43
Corner taken by Anthony Barry. Chris Maxwell catches the ball.68:45
Corner taken by Anthony Barry from the right by-line. Ian Miller manages to make a clearance.66:28 Substitution
Substitution (Forest Green) makes a substitution, with Magno Vieira coming on for Danny Wright.65:11
Harrison Dunk takes a shot. Blocked by Matthew Barnes-Homer.64:46
Corner taken by Ryan Donaldson from the right by-line.64:03 Substitution
Substitution Nathan Arnold on for Kwesi Appiah.63:24
Adam Cunnington takes a shot. Sam Russell catches the ball.62:03
Danny Wright concedes a free kick for a foul on Tom Champion. Chris Maxwell takes the free kick.60:38
Al Bangura gives away a free kick for an unfair challenge on Luke Berry. Chris Maxwell restarts play with the free kick.59:47
Danny Wright challenges Ian Miller unfairly and gives away a free kick. Chris Maxwell restarts play with the free kick.59:18
The assistant referee flags for offside against Adam Cunnington. Sam Russell restarts play with the free kick.58:01
Richard Tait concedes a free kick for a foul on James Norwood. Dale Bennett restarts play with the free kick.56:33
Assist by Dale Bennett.56:33 Goal scored
Goal! - Yan Klukowski - Cambridge 2 - 1 Forest Grn Yan Klukowski grabs a goal with a left foot finish. Cambridge Utd 2-1 Forest Green.55:00 Substitution
Substitution James Norwood joins the action as a substitute, replacing Andy Mangan.52:54 Goal scored
Goal! - Tom Champion - Cambridge 2 - 0 Forest Grn Tom Champion scores. Cambridge Utd 2-0 Forest Green.52:20
Corner taken by Ryan Donaldson.51:34
Corner taken by Ryan Donaldson.51:06
Harrison Dunk sends in a cross. Clearance by Eddie Oshodi.48:49
Jamie Turley gives away a free kick for an unfair challenge on Adam Cunnington. Centre by Ryan Donaldson. Header by Josh Coulson misses to the right of the target.47:47
Free kick awarded for an unfair challenge on Chris Stokes by Ryan Donaldson. Chris Stokes produces a cross. Andy Mangan takes a shot and missed to the right of the goal.45:01
The referee gets the second half started.45:01 Substitution
Substitution Yan Klukowski replaces Matt Taylor.44:55
Anthony Barry fouled by Tom Champion, the ref awards a free kick. Free kick taken by Sam Russell.43:15
Unfair challenge on Dale Bennett by Harrison Dunk results in a free kick. Free kick taken by Sam Russell.42:18
The referee blows for offside against Andy Mangan. Chris Maxwell takes the free kick.42:03 Half time
Half Time The whistle is blown to end the first half.40:13
Richard Tait takes a shot.38:18
Adam Cunnington takes the chance to get an effort at goal and missed to the right of the net.36:39
Free kick awarded for an unfair challenge on Dale Bennett by Harrison Dunk. Free kick taken by Sam Russell.31:44
Jamie Turley goes into the referee's book.31:44 Booking
Anthony Barry takes a shot. Chris Maxwell catches the ball.30:54
Chris Stokes crosses the ball. Clearance made by Ian Miller.27:39
Free kick awarded for an unfair challenge on Adam Cunnington by Eddie Oshodi. Free kick crossed by Harrison Dunk. Chris Stokes makes a clearance.27:17
The assistant referee flags for offside against Matthew Barnes-Homer. Free kick taken by Chris Maxwell.26:36
Harrison Dunk takes a shot and went wide left of the target.25:18
Kwesi Appiah takes a shot. Sam Russell safely holds on.24:32
Matthew Barnes-Homer has an effort at goal and missed to the right of the goal.22:13
Corner taken by Al Bangura.19:04
Foul by Ryan Donaldson on Matthew Barnes-Homer, free kick awarded. Chris Stokes takes the free kick. Greg Taylor produces a cross. Clearance made by Adam Cunnington.12:41
Adam Cunnington fouled by Eddie Oshodi, the ref awards a free kick. Free kick crossed by Richard Tait. Eddie Oshodi manages to make a clearance.11:23
Kwesi Appiah challenges Dale Bennett unfairly and gives away a free kick. Anthony Barry takes the free kick.10:47
The referee blows for offside. Sam Russell restarts play with the free kick.9:31
Free kick awarded for a foul by Matthew Barnes-Homer on Adam Cunnington. Richard Tait takes the free kick.4:29
Corner taken by Harrison Dunk. Free kick awarded for an unfair challenge on Jamie Turley by Ian Miller. Sam Russell restarts play with the free kick.0:56
The assist for the goal came from Richard Tait.0:56 Goal scored
Goal! - Luke Berry - Cambridge 1 - 0 Forest Grn Luke Berry scores with their right foot. Cambridge Utd 1-0 Forest Green.0:00
The referee starts the match.
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