Blackpool took an 18th-minute lead through Mark Cullen, who tapped in Bright Osayi-Samuel’s low cross from five yards.
Henry Cameron almost scored early on and Jack Redshaw somehow missed his kick from five yards with the goal gaping.
But the Seasiders were ahead for only four minutes as Alex Gilbey equalised with a superb shot, which flew into the top corner from the edge of the area.
Colchester’s Chris Porter went close with a header and Gavin Massey was denied by goalkeeper Colin Doyle after being sent through on goal by George Moncur.
But Blackpool restored their lead in first-half stoppage time through Cullen, who drilled in his second through a crowded penalty area.
Colchester started the second half well and equalised in the 57th minute when Ambrose converted Massey’s cross from five yards.
Massey missed a good chance to win it for the U’s shortly after as the points were shared.