Erling Haaland's early goal proved the winner on the day.
Guardiola later said: "I prefer to be top than not being top but it’s not the point.
“Look what happened today. Aston Villa dropped points (at home to Bournemouth) and Brighton dropped points (at home to Wolves) because it’s so difficult.
“We won at Wolves in minute 94/95.
“Today we created chances and we could have scored two or three goals, the expected goals is much better.
“But I have to admit it was a demanding game for us. Such a demanding game for us.”
On Haaland, he continued: “Many times it happened. It’s not the first time that thanks to Erling we won the game.
“I would say he scored the goal to win the game. It was important at the start.
“The first 15 or 20 minutes of the second half was excellent and in that moment we should have killed the game.
“I would say we were a little unfortunate with high pressing but at that moment they would drop a lot.
“That’s why when they had the ball they struggled to arrive in the final third. We created chances to score goals and the result is fair.
“But today Southampton demanded a lot from us.”