The striker scored twice to take his tally to 44 goals for the season with 30 of those in the Premier League alone.
His total is now the joint-most ever by a Premier League player in all competitions in a single campaign, equalling Ruud van Nistelrooy in 2002/03 and Mohamed Salah in 2017/18.
Haaland is the first City player to reach 30 league goals in a season since Francis Lee in 1971/72 and is closing on the record of 34 goals in a Premier League seasons set by Alan Shearer and Andy Cole.
His figures are drawing comparisons with Lionel Messi and Cristiano Ronaldo and Guardiola can understand why.
“Erling knows the other two guys dominated in two decades - not just one or two years, two decades, scoring and winning titles and doing absolutely everything,” the boss said.
“I think football is a better place mainly thanks to Cristiano and Messi. For our business, the attraction of these two guys competing helped us.
“Erling is just 22-23 years old, arriving in the toughest league in the world - I can talk because I’ve been in other leagues - and doing it is remarkable.”
Haaland came back into the side after missing the 4-1 victory over Liverpool and made another telling contribution.
He scored the first on the stroke of half-time when it looked like the sides would go in goalless before adding a stunning third with a spectacular volley.
“I would not say we were bad but I give a lot of credit to Southampton, their game plan was brilliant,” Guardiola said.
“ Erling is here for these types of games. He has a big heart and he was on the end of the assist from Kevin [De Bruyne]. His ability is incredible.
“We adjusted something in the first half and started the second really well and started much better.
“If it was 0-0 it would’ve been completely different. But, our game second half was much better.”
Asked if he could emulate Messi and Ronaldo, Guardiola added: “I think the pressure he has is high, like the pressure that Messi had or Cristiano had.
“He has that if he doesn’t score two or three goals it’s ‘what happened?’ The thing is he scored. Not all the time two or three goals.
“The numbers he has right now at his age are unbelievable. Unbelievable.”
