Messi brought up his 100th goal in Europe's premier club competition with a brace in the 3-0 second-leg win at Camp Nou on Wednesday.
The Argentina star also set up Ousmane Dembele as Barca sealed a 4-1 aggregate win to move into the last eight.
Iniesta, who came off before the hour-mark after starting despite a hamstring concern, lauded Messi for his latest masterclass.
"It's what we always talk about. Leo makes the difference in every game. It's a blessing," he told beIN SPORTS.
"I hope we can get closer to this Champions League. We've taken another step."
The win saw Barca reach the Champions League quarter-finals for the 11th consecutive season – the longest run in the competition's history.
Iniesta believes Ernesto Valverde's men are capable of capturing the trophy for a sixth time – and first since 2015 – this season.
"It's always a motivation to win the Champions League but it's always complicated. A bad game leaves you out," he said.
"The challenge is to minimise the mistakes because I think we have the team and the form to win it."