Messi tore through a hapless Bayer Leverkusen in their round of 16 second leg at the Nou Camp as holders Barca crushed the German side 7-1 to advance to the quarter-finals of Europe's elite club competition 10-2 on aggregate.
The 24-year-old's stunning opener and his third goal were particular highlights, each a wonderfully executed chip over Leverkusen goalkeeper Bernd Leno, first with his stronger left foot and then with his right.
"You won't see anyone like him in your lifetime and neither will I," Guardiola said at a news conference.
"We witnessed one of Messi's special nights tonight, it's a gift and I will always be able to say that I coached him," the former Barca and Spain midfielder added.
"The only credit I can take is that I always put him in the team and we just try to make sure he gets the ball. After that our task is done.
"The throne belongs to him and only he will decide when he wants to relinquish it."
Messi now has 12 goals in seven Champions League appearances this term, equalling the record for a single season he shares with former Manchester United striker Ruud van Nistelrooy. He has 49 in the competition overall.
His tally of 228 goals for Barca is only seven short of the club record set over 17 seasons by Cesar Rodriguez, while Messi is in his eighth campaign with the Spanish, European and world champions.
"Messi already deserves a tribute because it's incredible that he is seven short of Cesar at the age of only 24," Guardiola said.
"He is unique for his innate talent and his capacity to compete and he teaches us how to compete too."
Ten players managed the feat of scoring five goals in a match in the old European Cup but Messi is the first to do so since the Champions League replaced it from the 1992/93 season.
