Watford moved back into seventh temporarily and moved onto 50 points thanks to a late Andre Gray goal to gain the Hornets a point.
Southampton, meanwhile, took a big leap towards securing their Premier League survival courtesy of the fastest ever Premier League goal.
Story of the game
Shane Long played a vital role for the away side as he opened the scoring after a stunning 7.69 seconds - the quickest Premier League goal in history - following his block of Craig Cathcart's attempted long ball downfield, before chipping the ball over Ben Foster.
Watford very nearly had an immediate response to the fast opener, as Gray had a shot well saved by Angus Gunn, before the Englishman put his follow-up header over the bar.
The home side kept up their momentum briefly as they tried to find a goal back following the earlier sting, as the in-form Gerard Deulofeu put his attempt at goal narrowly wide.
After that, it was nearly all Southampton for the rest of the first half and much of the match. Long could have had his second if he didn't tip James Ward-Prowse's free-kick wide; before Foster was sent into action to deny Nathan Redmond, whose shot was tipped onto the post by the goalkeeping veteran.
Ryan Bertrand was the next player to strike the woodwork, as the Englishman failed to convert Redmond's incoming cross.
On the other side of half time, Watford started the brighter of the two teams, with some momentum again, but the Saints' steady back line was too difficult for the Hornets to break down.
The momentum died down quickly, however, and it looked as if Watford would be heading home from Vicarage Road with no points for a second consecutive game, following their narrow and undeserved 1-0 defeat against Arsenal last Monday.
It nearly got worse for the home side, as Ward-Prowse's free-kick was saved once again by Foster, who tipped it around the near post with 10 minutes to go.
However, Watford's desperation did once again turn into a good patch - the tiring squad very nearly found an equaliser after 88 minutes through clever footwork between Deulofeu and Gray, but Maya Yoshida did enough to stop Gray getting the shot away.
But Watford fans got something to celebrate about as the ball fell kindly to Gray inside the box, who converted powerfully from close-range to send Watford up to 50 points for the season.
Ralph Hasenhüttl's men will feel robbed, but the Saints' chances of being relegated have fallen significantly with what will probably turn out to be a vital point on the road.
Takeaways from the game
Watford lacking without Deeney
The one area where Watford were seriously lacking tonight was in attack. Before the Hornets' trip to Huddersfield Town on Saturday, Deulofeu and Gray hadn't worked up front as a pair at all. Javi Gracia has played captain Troy Deeney nearly every game this season, and it is clear that the striker has made a profound impact, with his hold up play being significant to Watford's game plan.
His suspension following an elbow to the face on Arsenal's Lucas Torreira last week may end up deeply costing the Hornets seventh place come the end of the season. It is a wonder whether Javi Gracia will resort to playing Isaac Success alongside Deulofeu for their very tough game on Saturday against a Wolves side also looking for Europe.
Earlier in the season, the pairing started together at Molineux Stadium in an impressive 2-0 victory. However, it is without a doubt that with the omission of Deeney, Watford may struggle yet again.
When Doucouré plays well, he is vital for Watford
Watford's 2017-18 player of the season, Abdoulaye Doucouré, was great in the win over relegated Huddersfield Town last weekend, but he lacked an awful lot tonight. Misplaced passes is not something necessarily regarded with the Frenchman, but today it certainly was.
When he plays well, Watford tend to have a strong performance, with his influence in bringing the ball forward and key interceptions being huge in each game. When he has a weak performance, like tonight, Watford lack much creativity.
A very fortunate point under the circumstances for the Hornets, undeniably, especially with the in-demand midfielder's poor showing tonight.
Robbed Saints should feel positive
Whilst Southampton will feel robbed of three points, they should look at the bright side. Hasenhüttl has managed to turn the Saints around, from impending relegation to pretty much avoiding it.
He has earned the side key points this season - and their 1-1 draw tonight is another one. Watford's form against non-top 6 sides has been immense; only losing three games all season when playing teams outside of the 'Big 6', and their last defeat coming on the first weekend of December. The Saints were a whisker away from breaking that record. A bright season is shaping up for next year, where they will surely be playing Premier League football again.
Up next
Watford have a huge match in the race for 7th place as they host Wolves at Vicarage Road on Saturday at 3:00pm, with the winner - if there is one - looking certain to finish in the final Europa League spot.
Southampton, meanwhile, will look to mathematically confirm their relegation survival in a south coast derby against Bournemouth at St. Mary's at the same time.