Southend remained top of League Two by beating promotion rivals Oxford.
The visitors dominated the first half with Luke Daniels denying Peter Leven three times but Southend led on half-time when Mark Phillips headed home.
Michael Timlin squandered a great chance to double the Shrimpers' lead and U's right-back Damian Batt levelled with a header from Leven's centre.
But Hall scored the winner for the hosts, cutting inside to fire home from 25 yards out.
The result takes Southend two points clear of second-placed Crawley, while Oxford drop to seventh, nine points behind the Shrimpers.
The two sides meet again, this time at the Kassam Stadium, on Tuesday in the Johnstone's Paint Trophy.
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Southend manager Paul Sturrock told BBC Essex:
"To be fair, a lot of people will walk away knowing that the better team today lost.
"But sometimes that's the essence of successful football. When you are not playing so well, and there's an edge missing, you roll up your sleeves and give even more.
"It was one of those days, the boys were very disappointed with what they churned out in the first half, we were much more solid in the second half."
Oxford United manager Chris Wilder told BBC Radio Oxford:
"The team has played ever so well at the league leaders. It was a real pressure game, the biggest game of the season and for 40 minutes I thought we bossed it and dominated the match but as always it's what happens in both boxes.
"I think the referee played a part because we certainly should have had two penalties and he's given a soft free-kick for their equaliser.
"We should have dealt with the ball better and the header on the goalkeeper could have done a little bit better for my liking.
"To come in at half-time behind was incredible, let alone being on level terms."