Andrew Bond's 89th minute goal earned Colchester victory against League One newcomers Gillingham.
The reigning League Two champions should have taken the lead in the first half but Danny Kedwell crashed his shot off the woodwork.
U's keeper Sam Walker was forced in to action by Charlie Lee and Chris Whelpdale as the hosts pushed on.
But it was Colchester who grabbed all three points as substitute Bond drilled home late on.
VIEW FROM THE DRESSING ROOM
Gillingham manager Martin Allen tells BBC Radio Kent:
"We had some good chances to win but as the game progressed they did also. We'll just have to take that one on the chin.
"I'm not sure we deserved to lose. It was a big game for our players and they need a bit of help going into the unknown.
"It's always a bit different first game of the season, especially when you knock the ball about the way they do.
"I thought they all played well. There was high expectancy. We have to dust ourselves down and not be too disappointed."
Colchester manager Joe Dunne tells BBC Essex:
"It's a difficult place to come, good club, good fans, and I thought we did a job today and were tremendous. Every single one played to their limit - we used the substitutes wisely and had a plan.
"We talked about the resilience from last year. We defended 20 plus set plays, long throws into the box, corner kicks into the box and I thought we did very well and deserved to win.
"We analysed every goal they scored last year, we spoke about concentration and we defended the box exceptionally well at set pieces.
"When the goal came, it looked like it was coming. We got in and around their back four countless times and I think if we had scored more I don't think anyone could have complained."