Leyton Orient picked up a much-needed point away at Colchester thanks to Jimmy Ryan's last-minute equaliser.
The U's, who had already seen Ian Henderson hit the post, went in front through Anthony Wordsworth's close-range finish after poor defending.
Dean Cox struck the woodwork and blazed over from close in as the O's pushed on in search of an equaliser.
With time running out Smith levelled when he tapped home from substitute George Porter's low cross.
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Leyton Orient boss Russell Slade told BBC London 94.9:
"I thought we dominated long periods of the second half. Although it was a fairly even first half, how we didn't get a penalty is beyond me.
"But to fight back the way we did and create four great openings in the second period, we were unfortunate not to win.
"Even if we'd lost I would have been proud of what we did. Hopefully we put a bit of pride back into the shirt today."
Colchester United manager John Ward told BBC Essex:
"We didn't play as well as we did in the first (half) and they lifted their game.
"It was pretty ding-dong in a sense, they had their spell, we had our spell, we couldn't find a goal and they got one at the death.
"I can't deny a draw in the game, that's probably about the right result."