SOMERVILLE -- Michael Capuano was looking downright congressional, walking into the Rosebud Diner in Davis Square yesterday in his crisp white shirt and dark red necktie, surprisingly fresh after only a few hours of sleep.

People looked up from their tuna melts and cups of minestrone to congratulate this new celebrity -- the mayor of Somerville, who became the last-minute choice of so many voters in Tuesday's 10-way Democratic primary for the 8th Congressional District that he is suddenly empowered to follow in the footsteps of John F. Kennedy and Thomas P. "Tip" O'Neill Jr.

Though Capuano held a one-point lead over former Boston mayor Raymond L. Flynn in polls before Tuesday's voting, he wound up beating Flynn 23 percent to 18 percent, with the others bunched up behind Flynn. In earning his 19,301 votes, his powerful organization made sure the Somerville base was a solid foundation -- almost 40 percent of his support came from his hometown -- but he drew surprising strength across the district, as voters settled on him as the alternative to others. Although he did not carry another city in the district, he pulled more than enough from his rivals to win the nomination. Capuano will face Republican C. Phillip Hyde and Independent candidate Anthony Schinella in November's general election.