Sam Gallagher helped Blackburn Rovers boost their Championship survival bid, as he played a pivotal role in their 1-0 home win over Derby County.
Gallagher, who played the full match, was fouled for the decisive penalty in the second half, as Craig Conway converted from the spot to give Rovers all three points.
The Saints striker had twice gone close in the first half, only to be denied by Scott Carson.
However, he played a big part in the breakthrough, as he was fouled in the area by Alex Pearce, in the 58th minute, allowing Conway to convert.
Gallagher was later kept out again by Carson, but Rovers’ solitary goal was enough for a win that puts them 22nd in the table, in the relegation zone only on goal difference.
They have now taken four points from their last two games, following last Friday’s 1-1 draw at Burton, in which Gallagher came off then bench in the second half, and they now head into back-to-back home games with Wigan and Cardiff.
Elsewhere on Tuesday night, Jason McCarthy was due to be in action for Walsall, but their home League One clash with Chesterfield was postponed due to a waterlogged pitch.
It means the Saddlers, who are 13th, have to wait until Saturday’s home game with Oldham for the chance to bounce back from last weekend’s 1-0 defeat at AFC Wimbledon, in which McCarthy played the full game.
In Spain, Saints keeper Paulo Gazzaniga started for Rayo Vallecano in their latest Segunda match, away to Getafe, on Saturday, and was on course for a clean sheet until Chechu Dorado’s own goal in the last minute gave the hosts a 1-0 win and left Rayo 19th in the standings.