Forster kept a sixth successive clean sheet since returning from 10 months out with a knee injury as a Shane Long header put Southampton back in the top six.
Midfielder Romeu has no doubts that the three-times capped Forster should be in Roy Hodgson’s England squad for Euro 2016.
“Of course, Fraser now is on top. He is one of the best in this league and one of the best in Europe.
“Fraser deserves all the compliments he gets, as does the defensive line. It is all about teamwork and we are all doing our jobs in that area.
“Fraser has saved us many times, but the three at the back have dealt with all crosses and one-on-one situations.”
Swansea are three points above the relegation zone after suffering their first defeat under Francesco Guidolin.
The Italian had previously overseen a win and two draws, but Long added to Swansea’s concerns over conceding goals at set-pieces when he was left unmarked eight yards out to dispatch James Ward-Prowse’s cross.
“When the cross comes in we should probably be a bit tighter,” said Swansea skipper Ashley Williams.
“It’s been disappointing in the last couple of weeks because we didn’t get the wins [against West Brom and Crystal Palace] that would have eased it.
“This is another disappointment, but we need to go again.
“We have to concentrate on what we need to do and get out of trouble.”
Fabianski, Rangel (Naughton 67), Fernandez, Williams, Taylor, Ayew, Cork, Britton (Gomis 73), Routledge (Barrow 61), Sigurdsson, Paloschi.
Forster, van Dijk, Fonte, Bertrand, Steven Davis, Ward-Prowse, Clasie, Romeu (Cedric Soares 63), Targett (Yoshida 86), Long, Pelle (Austin 74).