Sutton were relegated despite a thrilling 4-4 draw against fourth-placed MK Dons, while Crawley leaped into the play-offs at Barrow's expense on the final day.
It was always going to be an uphill task for Sutton, who needed a win, a Colchester loss and a five goal swing to survive. They showed great fighting spirit at least, going 2-0 down, then 3-1 down and then 4-2 down before scoring two late goals to earn a draw.
Colchester were leading Crewe 1-0 until stoppage time, when the visitors equalised, with the draw enough for both to secure their goals; survival for the U's and play-offs for the Railwaymen.
They finished the season sixth and will play Doncaster in the play-offs, who looked set to make it 11 straight wins at Gillingham before their goalkeeper Timothee Tutala-Lo was sent off for handling the ball outside his area, the Gills taking advantage by pulling two goals back in quick succession to earn a point.
Crawley were the big winners on final day as they beat Grimsby 2-0 while Barrow could only draw with Mansfield, meaning the former leapfrogged the latter to claim the final play-off spot. They will face MK Dons.
Bradford were also in with a chance of snatching a play-off spot, and they did their bit by beating Newport 4-1 for a fifth straight win, but they needed both Barrow and Crawley not to win.
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