Mitt Romney boosted his prospects for becoming the US Republican presidential nominee by winning six states including the coveted prize of Ohio on Super Tuesday.
But he failed to land a knockout blow against his main rival, Rick Santorum, who won three contests and barely lost Ohio. Newt Gingrich kept his candidacy alive by winning his home state of Georgia.
The mixed results suggest Mr Romney, despite padding his lead in the tally of delegates who will pick the nominee, is still unable to win over some conservatives and rally the party behind him.
With Mr Santorum and Mr Gingrich energised by their wins, the often-acrimonious race is likely to continue for weeks or months, perhaps weakening the eventual nominee and benefiting Barack Obama, whose standing in opinion polls has improved.
Mr Romney scored a home-state win in Massachusetts, where he served a governor, to go with primary victories in Vermont and in Virginia – where neither Mr Santorum nor Mr Gingrich was on the ballot. He later added the Idaho and Alaska caucuses to his column. Mr Santorum won the primaries in Oklahoma and Tennessee and the North Dakota caucuses.
But the most closely watched contest was Ohio, a heavily populated Midwestern industrial state. It was a test of strength for Mr Santorum, who was a US senator from neighbouring Pennsylvania.
With 99 per cent of Ohio’s precincts reporting, he had 38 per cent to Mr Santorum’s 37 per cent, an uncomfortably close margin for a candidate who had spent nearly four times as much money as his rival in the state.
But Mr Santorum is falling further behind Mr Romney in the delegate count and it is not clear how he can catch up. Moreover, Mr Gingrich, the former speaker of the House of Representatives who represented a suburban Atlanta district in Congress for two decades, insists he will stay in the race after his win in Georgia and could split the conservative vote as he vies to be Mr Romney’s main rival.