Gareth McKeown's late winner against Portadown means second-placed Crusaders are now just six points behind Premiership leaders Cliftonville.
McKeown blasted in the 85th-minute winner from Paul Heatley's pass seconds after Portadown's Keith O'Hara had been sent-off for two yellow cards.
There was confusion as referee Alan Black showed O'Hara the second yellow but did not follow it with a red.
However, after consulting an assistant, the ref dismissed the Ports skipper.
Match official Black upset the visitors in the first half when he disallowed a Tim Mouncey goal.
Mouncey had headed in at the back post from a Ross Redman corner in the 27th minute but it was ruled out for a foul.
In the second half, McKeown glanced a header wide and Jordan Owens was also off target with a couple of headed efforts.
"I think we were on top for most of the game," said defender McKeown afterwards.
"It was a big game for us. We had to be patient and it paid off as we got the goal.
"We have been trying to make Seaview a fortress and we enjoy playing for the fans here."