The Barcelona coach hailed the Argentine's performance in their 4-1 first leg Copa del Rey quarter-final victory over Levante after he assisted three of his side's goals
The Catalans had to come from behind as Nabil El Zhar gave the hosts an unexpected lead, but Messi played a pivotal role in overturning the score as he helped Cristian Tello grab a hat-trick in the 4-1 win.
And Martino hailed the performance of the 26-year-old. who was making his 400th appearance for the club.
"It is true that when Leo plays he can change the game in our favour," he is quoted as saying by Sport.
"When we are operating in tight spaces and when the opposition are closing us down, players like Messi can help us to create openings.
"He has provided three assists tonight and has been the key to our successful performance."
El Zhar exposed some weak Barcelona defending to give Levante a shock lead as the visitors started off slugglishly.
But in the second half they found their rhythm and Messi and Tello wrecked havoc against the Levante backline, forcing a calamitous own goal from Juanfran to level the score before Tello bagged his hat-trick.
"In the first half we lacked movement and mobility. Levante were doing well and playing with men behind the ball. Luckily they made a mistake in the second half and from then we began to wear them down," Martino continued.
"As the minutes passed and we got to the latter stages that was something we used to our advantage."
The Barca coach was full of praise for Tello, who grabbed his first hat-trick in Blaugrana colours.
"There some players who show what they can do over 90 minutes and others who demonstrate it in 15. Cristian is one of those who demonstrates what he does in shorter spurts and that can be difficult," Martino said.
“But this match has served him well. The confidence that you can generate from good performances is significant and he definitely needed a game like this.
"We have a very large squad of players and to me it is logical that they should all get a chance to play. Today we had a bad first half and a good second half. We thought that these were the players we should call upon despite the two draws we have had recently."