Manager Gary Johnson made two changes to his starting eleven with Ishmael Miller and Jamie McAllister starting.
The hosts were the first team to test either of the keepers with Jay Rodriguez forcing Marek Stech into a diving stop.
On 18 minutes the former Burnley man thought he had opened the scoring for the Saints but the Glovers had the woodwork to thank when his strong header rebounded off the cross bar and away to safety.
Southampton took the lead when a corner from the left was swung into the penalty area where Shane Duffy was adjudged to have handled in the area. Referee Phil Dowd had no hesitation in putting his whistle to his lips to award the home side a penalty. Guly do Prado made no mistake from 12 yards in sending Stech the wrong way.
With just over five minutes of the first have remaining the hosts had keeper Davis to thank for keeping the score at 1-0. Good link up on the left between Grant and Ralls get space in the area for the latter to cross to James Hayter, but the strikers effort hit Davis and he gathered comfortably at the second time of asking.
The Glovers started the second half brightly and nearly equalised when Luke Ayling picked up a loose ball just outside the area. The right back jinked his way past two defenders to fire a left footed effort at goal. Just as he thought he had scored his second goal of the season, keeper Davis dived across goal to tip his goal bound shot wide.
On the hour Town keeper Stech was again called into action this time the big shot stopper got down well to his left to deny substitute Sam Gallagher’s long-range effort.
On the 70th minute the home side doubled their advantage when Gallagher drifted past the Town defence to coolly slot past Stech from ten yards.
In the dying minutes Stech denied the home side a third goal with a superb one handed save to deny substitute Steven Davis.