Skipper Tommy Rowe scored the decisive penalty kick to send Posh to Wembley for the first time in 14 years.
The scores were level and one successful spot kick would send Peterborough United to Wembley Stadium in the Johnstone's Paint Trophy final.
The responsibility fell on the shoulders of the skipper, Tommy Rowe. Fans nervously held their breath as the rest of the squad gathered arm in arm on the half way line.
The midfielder said afterwards: 'It was a big moment obviously because I knew the enormity of the spot-kick, but I knew where I was going to put it and was obviously delighted to see the ball hit the back of the net.
'It was a great feeling and to celebrate with the rest of the squad in front of the fans was a special moment. I think over the two legs, we just about shaded it and the lads are very much looking forward to playing at Wembley Stadium.
'I am sure that can spur us on in the league as well. We wanted to do well in this competition and the manager definitely got it across just how much it would mean to play at Wembley,' Rowe said.
Striker Britt Assombalonga was named the Sky Sports Man of the Match after his equaliser in normal time sent the tie to penalties. It was the former Watford man's 24th strike of an excellent campaign.