Vestergaard's red card was his first of his 252-game career
Southampton held Leicester to a draw despite playing more than 80 minutes with 10 men to frustrate the Foxes in their push to clinch a top-four finish.
Jannick Vestergaard was controversially sent off after just 10 minutes when his tackle on Jamie Vardy was deemed to have denied the Leicester striker a goal-scoring opportunity.
Vestergaard, on the edge of his box and the last defender, got the ball with a lunging tackle but referee Robert Jones deemed his follow-through on to Vardy's ankle had prevented the striker running in on goal.
That decision set the game's pattern, Leicester probing while Southampton defended deep, but it was the Saints who took the lead in the 61st minute.
James Ward-Prowse scored from the penalty spot after Kelechi Iheanacho had blocked Stuart Armstrong's effort with his arm raised up by his head.
Jonny Evans headed in Iheanacho's cross eight minutes later for the equaliser but under near-constant pressure Southampton's defence held firm.
Goalkeeper Alex McCarthy brilliantly denied Vardy with his right boot from close range in the final 10 minutes.
The point takes Leicester eight points clear of fifth-placed West Ham having played a game more but they have a difficult end of the season to come.
Southampton edge 10 points clear of the relegation zone as they close in on guaranteeing their safety.
Reaction from Southampton v Leicester
Leicester frustrated on south coast
- 0.1 Leicester frustrated on south coast
- 0.2 Southampton show much-needed resilience
- 0.3 'Not a red card' – manager reaction
- 0.4 Evans' goal-scoring streak – the best stats
- 0.5 What's next?
- 1 Southampton
- 2 Avg
- 3 Leicester City
- 4 Avg
- 5 Line-ups
- 6 Match Stats
- 7 Live Text
The point takes Leicester closer to their goal of securing Champions League football next season but, having played against 10 men for so long, they should have ended the night with a 10-point cushion over fifth place.
Wilfried Ndidi dragged a shot wide from the edge of the box and Iheanacho came agonisingly close to meeting Marc Albrighton's cross in the closing stages.
Before Evans' equaliser, however, they had had created little despite dominating possession.
With Southampton in a defensive mindset visiting manager Brendan Rodgers replaced defender Wesley Fofana with forward Ayoze Perez at half-time but many of his side's 22 shots came from long distance.
It was Iheanacho, who has been Leicester's star in attack with 12 goals in nine games, who foolishly closed down Armstrong's shot with his arm raised for Southampton's penalty. He did at least redeem himself with a fine left-footed cross for Evans' equaliser.
Leicester are still in a fantastic position for a top-four finish but their slump at the end of last season, plus the fact they have trips to Manchester United and Chelsea to come as well as a game against Tottenham on the final day, means Champions League qualification is not yet certain.
Southampton show much-needed resilience
For Southampton this was a morale-boosting result coming in a difficult run that had seen them lose 12 of their past 15 games.
The game briefly stopped in the 29th minute to allow Wesley Fofana to break his Ramadan fast
After the early loss of Vestergaard some might have feared a repeat of the 9-0 loss to Manchester United earlier this season when they went a man down early – or the defeat by Leicester last season by the same scoreline.
Instead, they produced an admirable defensive display that left manager Ralph Hasenhuttl visibly pleased at full-time.
Vestergaard made a mistake with an initial loose touch but his dismissal was harsh.
The centre-back clearly made contact with the ball before catching Vardy, admittedly making strong contact with the striker's ankle.
It was deemed by referee Jones that his follow-through had prevented Vardy running on to the deflected ball, a decision confirmed by the video assistant referee, but Vestergaard's touch had diverted it back towards goalkeeper McCarthy, who said afterwards he thought he would have reached the ball first.
'Not a red card' – manager reaction
Southampton boss Ralph Hasenhuttl to BBC Sport: "Big credit. We can discuss the red card and for me how we bounced back was amazing. They had 80 minutes to score against us. The goal we conceded, but the rest was really well defended around the box.
Southampton 1-1 Leicester: Jannick Vestergaard did not deserve red card – Ralph Hasenhuttl
"Jannik Vestergaard has a bad touch and then plays the ball back to the keeper. The official explanation was it was 100% goal chance – for me Jamie Vardy never had the ball because the keeper was there. Maybe a foul because he caught him after but not a red card."
Leicester manager Brendan Rodgers to BBC Sport:
"When the opposition go down to 10 men we're normally good in those situations but you have to credit Southampton to show that resilience and to keep us out. Jamie Vardy is a warrior so he got up and Alex McCarthy made a great save from him."
Southampton 1-1 Leicester: 'A point towards where Foxes want to go' – Brendan Rodgers
Evans' goal-scoring streak – the best stats
Southampton are the first side to avoid defeat in a Premier League game when they had a man sent off inside the first 10 minutes since Leicester in March 2019 (2-1 win v Burnley, after a fourth-minute Harry Maguire dismissal).Leicester scored just once from 22 shots against Southampton, after scoring nine goals from 25 shots against them in this fixture last season.Southampton have dropped more points from winning positions than any other team in the Premier League this season (23).Leicester have failed to win consecutive Premier League away games for the first time since July 2020, when they were winless in their final eight away games of last season.James Ward-Prowse has been directly involved in 14 goals in the Premier League this season (8 goals, 6 assists), the most by a Southampton midfielder in a single campaign since Dusan Tadic in 2015-16 (19).Jonny Evans has scored two goals in his past three Premier League appearances for Leicester, as many as he had in his previous 95 games in the competition.Leicester striker Jamie Vardy hasn't scored in any of his past eight away appearances in the Premier League – his longest run of away games without scoring in the competition since September 2016 – February 2017 (10).Jannik Vestergaard's red card for Southampton (9:13) was the second-quickest sending off in the Premier League this season, with the quickest also being by a Saints player earlier this year (1:22 – Alexandre Jankewitz versus Manchester United in February).
Leicester host Newcastle on Friday 7 May in their next game (20:00 BST) – on paper the easiest of their remaining fixtures.
Southampton travel to Liverpool on Saturday 8 May (20:15 BST).
Player of the match
with an average of 8.22SouthamptonSouthamptonSouthamptonLeicesterLeicester CityLeicester City
Line-upsMatch StatsLive Text
1McCarthy2Walker-Peters35Bednarek4Vestergaard5Stephens19Minamino8Ward-Prowse17Armstrong23Tella10Adams11Redmond1McCarthy2Walker-Peters35Bednarek4VestergaardBooked at 10mins5Stephens19MinaminoBooked at 50minsSubstituted forDialloat 76'minutes8Ward-Prowse17Armstrong23TellaSubstituted forSalisuat 15'minutes10AdamsSubstituted forN'Lunduluat 90+1'minutes11Redmond
1Schmeichel3Fofana6Evans4Söyüncü27Castagne25Ndidi8Tielemans33Thomas10Maddison14Iheanacho9Vardy1Schmeichel3FofanaSubstituted forPérezat 45'minutes6Evans4Söyüncü27Castagne25Ndidi8Tielemans33ThomasSubstituted forAlbrightonat 69'minutes10Maddison14Iheanacho9Vardy
11Albrighton12Ward17Pérez18Amartey19Ünder20Choudhury21Ricardo Pereira24Mendy26PraetReferee:Robert Jones
Home TeamSouthamptonAway TeamLeicesterPossessionHome29%Away71%ShotsHome5Away23Shots on TargetHome3Away9CornersHome0Away10FoulsHome9Away13
Match ends, Southampton 1, Leicester City 1.