The Brazilian, who is now on loan with Premier League counterparts Newcastle United, scored his first goal for the club in the second minute of the Magpies' clash with Southampton at St. James' Park earlier today.
"Southampton Football Club can today confirm that it has parted company with First Team Manager Mauricio Pellegrino", a club statement read.
The latest 3-0 defeat at relegation rivals Newcastle on Saturday proved to be the final straw for the Southampton hierarchy, with the club in danger of being relegated from the top flight for the first time since being promoted in 2012. "The search for a replacement [is] already underway".
The Saints have endured a frustrating season under Pellegrino, who was only appointed last June.
It was entitled to be a tense and nervy affair on Tyneside with just one point and one place separating the sides in the table before kick off, but Rafael Benitez's men blew their opponents away to ease fears of them going down.
Former Liverpool defender Pellegrino had been under increasing pressure as the season progressed, with fans frustrated by his perceived defensive tactics and pundits accusing the players of not playing for him.
"We will do everything we can; I have said it before that the club cannot go down, we have to stay up".
"These games are ones you can not lose".
After that, he failed to really establish a place in the Chelsea team and things looked bad after a disappointing loan spell at Watford in 2016.
To rub salt in the wounds Puel is now flourishing at Leicester, who currently lie eighth.
Former Alaves coach Pellegrino did lead the south-coast club into the FA Cup quarter-finals, with the now-managerless side set to visit third-tier Wigan in the last eight on Sunday.