Going behind is no new experience for Rovers - it has happened in all but one game so far - and in a lively match Richard Walker put them level early in the second half.
There was often more energy than direction from both sides in the opening period and Hackett put in rather too much when he went down in the box early on under a challenge from Steve Elliott
Referee Alan Wiley was distinctly unimpressed by the appeal for a penalty and booked Hackett for diving.
The first genuine chance came from Rovers as Craig Disley broke from the midfield to make space on the left for a good cross. Walker connected well and keeper Billy Turley could only watch as his header flew inches wide of the left-hand post.
Another chance came Walker's way when his partner, Junior Agogo, swept inside Matt Robinson on the right to punt a centre into the goalmouth. A downward header bounced high and Turley reacted swiftly with a fingertip deflection for a corner.
In between, Walker had picked up a warning for backing into Chris Willmott as he faced a high ball from his defence.
Wiley was ruling the game decisively, although Oxford striker Eric Sabin felt hard done by when he blew up for a foul on him by Disley. Sabin had shrugged off the tackle and clearly felt he was in a position to go past Rovers' back line.
His anguish though was nothing compared to that expressed by Rovers' manager Ian Atkins when Hackett scored in first-half stoppage time.
No-one got in a tackle as Robinson sped down the left wing and Hackett was equally free to glance his header in off a post.
The equaliser was controversial as Walker went past Leo Roget to meet Ali Gibb's through ball. The Oxford defender clearly felt he had been fouled.