Nigel Adkins has been sacked as Southampton manager with Argentine boss Mauricio Pochettino installed as first-team manager.
Adkins joined Saints in 2010, taking the club from League One to the Premier League after successive seasons.
Southampton currently sit 15th in the Premier League, three points above the relegation zone but with executive chairman Nicola Cortese keen to take the club forward, former Espanyol boss Pochettino has been appointed.
"This decision has been made with the long-term ambitions of Southampton Football Club in mind," Cortese said.
"Whilst we acknowledge the contribution Nigel has made during the past two years, for the club to progress and achieve our long-term targets a change was needed.
"Mauricio is a well-respected coach of substantial quality who has gained a reputation as an astute tactician and excellent man manager. I have every confidence that he will inspire our talented squad of players to perform at the highest possible level.
"He also shares my belief that the most successful clubs are built by nurturing young players through a development system that provides a clear path to the first team, thereby creating a culture that keeps them at the club for the long term.
"This is an approach he has employed with great success in the past and I look forward to him bringing that experience and expertise to Southampton."
During three years at the Estadio Nornelia-El Prat, Pochettino led an Espanyol side blighted by limited finances and a series of high-profile sales to successive mid-table finishes, before being sacked in November with the club bottom of La Liga.
"This is the kind of opportunity that any coach would relish," Pochettino said. "Southampton is a club with great heritage, and an even more exciting future.
"There is a clear vision to take the club to a new era of sustained success in the Premier League, and beyond, which I'm delighted to be part of."
Unbeaten in their last five league matches, Adkins' final game in charge of Southampton saw them come back from two goals down against European champions Chelsea to grab a draw at Stamford Bridge.
Cortese committed to a series of big money signings in the summer transfer window, bringing in Uruguayan winger Gaston Ramirez and England Under-21 striker Jay Rodriguez for a club record fee.
And Adkins had seemingly lived up to the pressure, guiding Saints to five league wins this season, as well as impressive performances in defeat to Manchester City, Manchester United and Tottenham Hotspur.