Mitt Romney wins Illinois primary, increasing lead over Santorum Mitt Romney celebrates winning the Illinois primary. Photograph: Don Emmert/AFP/Getty The Republican presidential frontrunner, Mitt Romney, won an overwhelming victory over his main rival, Rick Santorum, in their Illinois showdown, the last realistic chance for the latter to mount a serious challenge. Santorum badly needed to pull off an upset but fell well short. Although the race is set to drag on for weeks yet, Santorum faces watching his hopes of the Republican nomination drift further and further away. Romney's unqualifed victory will boost the confidence of his team that he will be the eventual Republican nominee to take on Barack Obama for the White House in November. It was not just that he won but the scale of his victory. With more than 60% of the votes counted, Romney had 48% to Santorum's 34%. Ron Paul and Newt Gingrich largely bypassed Illinois and this was reflected in their poor showing, with Paul on 9% and Gingrich on 8%. Romney, speaking at an election night party in Schaumburg on the outskirts of Chicago, described it as "an extraordinary victory." He made no mention of Santorum and resisted the urge to call on him to quit - instead, as before when he has been on top, he has started behaving as if he is the presumptive nominee, devoting most of his speech to criticising Obama. He mainly reprised a speech on the economy he had delivered the previous day at the University of Chicago. Santorum, holding his election night party in Gettysburg, Pennsylvania, insisted he was battling on. In almost every speech he describes the election as being of lifetime importance. Inspired by Gettysburg, he went further, saying it was the most important since the one that heralded the civil war in 1860. Santorum is favourite to win the next contest, Louisiana, at the weekend but the calendar immediately after that looks more favourable for Romney. With 23 states left to go Romney is favourite to take the bulk of these, including the larger states California, New York and New Jersey. With each win Romney is piling up delegates to the party convention in August where the nominee will be formally chosen. The Illinois victory significantly expanded the gap between him and Santorum, with Romney taking the biggest share of the 54 delegates up for grabs. Illinois, more even than Super Tuesday earlier this month, appears to mark an important break in a campaign that has been running since 3 January. With Romney looking like the eventual nominee, US networks and other media organisations have already begun to scale back their coverage. The sense of weariness was picked up in exit polls, with about 30% of voters saying they would prefer to see the race over, even if it meant their candidate did not win. There is speculation that the race might not be settled by the summer and that the battle will continue into the convention. Even if that happened Romney would have by far the largest bloc and it is hard to envisage Santorum at that point being able to present himself as a viable alternative. Romney won heavily in Chicago and its densely populated suburbs, while Santorum drew his suppoort from the more conservative cities, towns and rural areas to the south. The exit polls showed the main issue was the economy on which Romney has been campaigning almost exclusively while Santorum, though he too campaigns on the economy, adds constitutional and cultural issues. The exit polls confirmed that economic issues were the main concern of about 80% of voters, with abortion named by only 12%. Santorum's remark on Monday that he did not care about unemployment possibly came too late to have a big impact on the election. A bigger mistake was Santorum devoting two days to campaigning last week in Puerto Rico where he lost badly, time that would have been better devoted to Illinois. Santorum suffered too from lack of cash. The Campaign Media Analysis Group estimated that Romney and the super political action committee backing him outspent Santorum and his super PAC by a staggering 18-1 on advertising. Many voters admitted they had been influenced by the ads but also said that an important consideration was electability, the best candidate to beat Obama, and Romney topped Santorum. Only 20% regarded as more important to elect a "true conservative," Santorum's main selling point. The lack of enthusiasm for either Romney or Santorum came through in the exit polls and is a potential problem for the November election. More than four out of 10 said they had reservations about the candidates.