By james art 
The left winger’s late goal helped the Saints off the table on a day where they were also indebted to goalkeeper Aaron Ramsdale’s heroics.
Everton’s Beto thought he had leveled minutes from time, but after a lengthy review, the effort was ruled offside as Russell Martin’s promoted side received a much-needed boost in their bid for survival.
The Saints’ theme of dominating possession continued as Everton struggled to break through the hosts’ well-organised structure in the early stages, with new boy Mateus Fernandes the key link between midfield and attack.
The 20-year-old summer signing from Sporting Lisbon drifted between the lines and constantly picked out Armstrong on the right, but the wide man struggled to get the better of marker Vitaly Mikolenko.
The Saints continued to play football that belied their 20th-placed position at the start of the weekend, with Flynn Downes putting Cameron Archer in behind only for the striker’s effort to narrowly miss the left-hand post, much to the relief of a well-beaten Jordan Pickford.
Everton were second best but with the level of play they were still very much in the race. Idrissa Gueye’s first strike from a corner early in the second half resulted in Ramsdale’s save spinning awkwardly into the roof of the net as Everton pushed forward in search of the opener.
The Caramels came close again in the 67th minute. Substitute Jesper Lindström swung in from the left, cut in and fired a right-footed shot that was met by the head of Michael Keane in the six-yard box. Miraculously, Ramsdale showed instinctive reflexes to touch the ball against the post, preserving the tie.
Ramsdale’s heroics continued as he began to outperform the opposite number and England number one Pickford. The former Arsenal man, who moved to the south coast for a reported £18m in the summer, produced another incredible stop, this time tipping Lindström’s free-kick over the bar.
Beto hit the post for Everton after 84 minutes and, typical of the end-to-end affair, Saints pounced at the other end to take the lead.
Yukinari Sugawara was unleashed on the right and a simple ball into the middle saw Armstrong sneak inside and bury his first try into the bottom left corner.
Beto thought he had salvaged a point with a late finish, but VAR saved the Saints as they earned an important and deserved three points.