Southend equalled their club record of 17 games unbeaten by holding Oldham in the FA Cup second round.
United's Bilel Mohsni had a header disallowed for a foul and Athletic took the lead when James Wesolowski struck from the edge of the area.
Oldham captain Dean Furman hit the bar before Ryan Hall levelled, firing into an empty net from 35 yards, after Alex Cisak had run out to clear the ball.
Mohsni had a second headed goal ruled out, for offside, to set up a replay.
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Southend United manager Paul Sturrock told BBC Essex:
"In the first half I played a solid formation, which didn't work. At half-time I knew I had to change things, which I did.
"I emphasised the things we needed to do in the game and they did that very well. It was a real good second-half performance, in the end they were hanging on.
"It's quite pleasing to see us rub shoulders with these types of teams and not look out of sorts."
Oldham Athletic manager Paul Dickov told BBC Radio Manchester:
"I was delighted with out performance first-half and the first 20 minutes of the second-half we were comfortable.
"Yet again we seem to be standing here and speaking to managers after games and we're talking about referees. If he's had a good game you don't talk about him.
"We're putting a nice little run together at the minute, we've got a bit of momentum which is important with the schedule coming up now."