A win in Illinois - Obama's home state -- was considered a must for Romney to bag Republican presidential nomination this summer.
However even after this big win, American media said that the deal is not done yet for Romney.
"Mitt Romney got a much-needed victory in Illinois on Tuesday night, but his triumph is unlikely to change the dynamics of the GOP presidential primary," The Hill said, adding that Santorum is favoured to win the next contestants.
The Republican presidential campaign now moves to the southern american state of Louisiana, which is headed by the Indian-American governor, Bobby Jindal.
According to a latest poll, Santorum lead Romney by 13 points in this state.
"Mitt Romney won Tuesday's Republican presidential primary in Illinois, a victory that widened his lead over his chief rival for the nomination and will likely provide a jolt of energy to his campaign.
"Despite the victory for Romney, the race is unlikely to dramatically shake up the basic geometry of the race," The Washington Post reported.
"Though Illinois is a major prize for Romney, who will claim the majority of the state's 54 delegates, the victory does not close the door on Rick Santorum, who will also win a portion of those delegates and has vowed to soldier on," the daily said.
It's the first time since 1988 that a Republican presidential primary has been relevant in Illinois, the Chicago Tribune said.
The other two candidates, Newt Gingrich and Ron Paul, had polled less than 10 per cent of the total votes.
