A first-half goal from Colin Daniel condemned Rovers to non-league football next season. With Northampton and Wycombe both securing wins, even the support of a 10,000-plus crowd was not enough to keep the Pirates in Sky Bet League Two.
A bad day for the hosts became even worse when police horses had to be summoned to deal with a pitch invasion from angry fans after the final whistle.
The goal the home fans were dreading came on 36 minutes when Anthony Howell crossed from the left and Daniel engineered space to hook a volley in off a post from 12 yards.
Rovers threw everything at their opponents in the second half and hit the woodwork twice through a David Clarkson header and a Mark McCrystal volley.
A devastated Clarke said: "Words cannot sum up how I feel. I have picked the team for the last eight games and we didn't get the required points so I take responsibility.
"In the dressing room afterwards I asked all the players to look at themselves and be honest about whether they had done enough over the course of the season.
"I can only apologise to our fantastic supporters. They have given us tremendous backing and it is awful not to have rewarded that."
Rovers chairman Nick Higgs also faced the press, and said: "It is the darkest day in the history of our club, but I can assure fans that we will be back.
"Our plans for a new stadium will not be affected and we were already planning a lot of changes for the summer, so that will not be altered either."
There were countless other near misses for a Rovers team who were hugely unlucky on the day.
Mansfield boss Paul Cox said: "You don't enjoy seeing grown men cry on the pitch at the end of the game. I asked my lads to play with pride, but we respect Bristol Rovers as a big club and I am sure they will be back.
"I know Darrell Clarke and can only imagine what is going through his head at the moment. We take no pleasure in sending a club out of the (Football) League. It's a harsh way to learn, but he will emerge a stronger person for it.
"The lads have shown a lot of pride and we will look to do better next season. Rovers have thrown the kitchen sink at us in the second half and we had to dig in."
- Sports & Recreation