Paul Anderson and Sam Baldock have put Bristol City on course to record their first home win since August.
The Robins have not been victorious at Ashton Gate in their last nine matches, but they lead Peterborough United, who are down to 10 men, at the midway point this afternoon.
Anderson broke the deadlock on five minutes when he found the net with a diving header from close range, following a good cross from Baldock.
Lee Tomlim was shown a straight red card seven minutes later for an alleged elbow on Greg Cunningham.
Posh responded well to losing Tomlin and they levelled the scores on 19 minutes when Grant McCann coolly converted from the penalty spot, after Tom Heaton had been penalised for a foul on George Boyd.
However, City regained the upper hand and restored their lead with eight minutes of the first half remaining.
Anderson found Baldock with a clever through ball and the former West Ham United forward beat Robert Olejnik with a cheeky lob.