The La Liga leaders overcame going a goal down to cruise to a victory which gave them a 10-point advantage at the top with a Luis Suarez hat-trick and debut league goal for Philippe Coutinho ensuring the three points.
"It's difficult to get used to, especially because we're talking about a player about whom we say we've seen it all, but Messi always surprises you," said Valverde.
Messi, who now has 30 goals in all competitions this season, had Valverde reaching for the superlatives for his free-kick which bamboozled Girona when he coaxed the ball along the floor instead of over the top and into the net.
"We all expected to see how he would get it over the wall but he hits it under. You see it and you think it's easy. Leo just makes it look easy, but it's not that easy," said the coach.
The match was also special for Messi from a personal point of view as it was the first since the death of his maternal grandfather at home in Rosario in Argentina.
Real Madrid, meanwhile, remain off the pace in third, despite a comfortable 4-0 victory over Alaves that saw Cristiano Ronaldo net a double and Gareth Bale back on the scoresheet.
Real coach Zinedine Zidane hailed Ronaldo's selflessness after the forward gave up the chance of a hat-trick by allowing Benzema to take a late penalty at the Santiago Bernabeu.
Zidane restored Bale to the starting XI to reunite the 'BBC' front line of the Welshman, Ronaldo and Benzema.
Ronaldo, whose first goal was created by a magnificent Benzema flick, stood aside in the 89th minute to allow the Frenchman to convert only his fourth league goal of the season.
"The gesture of Cristiano is very important," said Zidane. "After the game he played, Karim just needed to score a goal. He (Ronaldo) had opportunities, he scored twice. After there is this gesture of Cristiano for Karim. This proves that between them, there is a good atmosphere, a good relationship, and to win and continue what we're doing, it's super important."
The reigning champions' title hopes are all but over, with Real 14 points adrift of Barca, but a run of four straight wins has ended any worries of missing out on a Champions League spot.
"Confidence returns from playing these kinds of matches," added Zidane. "After our match against PSG (3-1 win in Champions League), we've been doing much better, maybe there was a missing part or something like that."
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