Will Randall struck a stoppage-time winner to secure promotion-chasing Sutton a 3-2 win over struggling Colchester.
Colchester took a third-minute lead when debutant Owura Edwards' 25-yard strike beat keeper Dean Bouzanis, after Brendan Wiredu had won possession well in midfield.
But Sutton equalised in the ninth minute through Isaac Olaofe, who followed up to score after Omar Bugiel's close-range effort had rattled a post.
Colchester goalkeeper Jake Turner pushed away Bugiel's effort soon after but the visitors restored their lead, in first-half stoppage time.
Freddie Sears slotted home from the spot after Louis John was adjudged to have handled in the area.
And the hosts equalised in the 64th minute through Olaofe, who headed home at the far post after substitute Richie Bennett had nodded Enzio Boldewijn's delivery across the face of goal.
And Randall hit Sutton's winner in the second minute of stoppage time when he drilled home a low shot from the edge of the area, from Alistair Smith's assist.