Martin Ling is still targeting automatic promotion after Torquay drew level on points with Crawley after a 1-1 draw at home to Crewe.
The Gulls were less than a minute away from victory when the Railwaymen's top scorer Nick Powell claimed his 15th goal of the season with a thumping 15-yard strike which puts Steve Davis' team within a point of clinching a play-off place.
United took the lead through a 54th-minute Danny Stevens shot from the edge of the area, but had a warning of what was to come when goalkeeper Bobby Olejnik saved Harry Davis' 76th-minute penalty.
Ling said: "If we knew we were going into the last game level on points with Crawley we would have taken that before the game. We got the goal but then to a certain extent we rode our luck a little bit - Bobby Olejnik saved a penalty and they hit the bar - and you thought this might just be our day.
"But in the end it turned out that it wasn't entirely going to be our day. The thing we have got to remember is that we have gone from being a point behind Crawley to level with them. Crawley are still in the pole position for third spot but they have to go to Accrington. We are second best and Southend are third.
"It's all going to go down to the last game of the season. Who could have predicted that? What I can predict is that we will give it our best shot again. The skipper Lee Mansell is in there telling the boys that they have got to lift themselves. There is still everything to play for and we go to Hereford in a better position than when we started this game."