Italian rider Boem was part of the breakaway which held off the charging peloton in the finale of the 200-kilometres route from Civitanova Marche to Forli along the Adriatic coast, Boem winning the stage in a time of four hours, 26 minutes, 16 seconds from compatriot Matteo Busato.
Alberto Contador (Tinkoff-Saxo) enjoyed an uneventful day to retain the overall leader’s pink jersey, with Porte’s bid for the maglia rosa hindered by the mishap 5km from the finish.
The Australian, who began the day 22 seconds behind in third, suffered a late and costly mechanical, losing 47 seconds to the Spaniard to slip to fourth in the general classification.
Porte’s fortunes would have been worse but for the sportsmanship of compatriot Simon Clarke. The Orica-GreenEdge rider gave Porte his wheel to help to minimise time losses.
A few members of Porte’s Sky team escorted him to the finish in a frantic effort to avoid more lost time.
Porte wrote on Twitter: “Not the best of luck for me today but guess it could have been worse. Ready to fight all the way to Milan! If that’s not Aussie mate ship then what is? Punctured and clarkey gave me his front wheel.”
Clarke added: “He punctured and obviously needed a hand. It could have cost him the Giro.” Porte now trails Contador by one minute nine seconds overall, with Fabio Aru, of Italy, the nearest challenger, three seconds behind. Aru’s Astana team-mate Mikel Landa, of Spain, is third, 46 seconds back.
Contador, who suffered a dislocated shoulder last week, played down rival Porte’s time loss, with plenty of racing remaining before the finish in Milan on 31 May.
“It was anything but an easy day,” Contador said. “Every day at the Giro can hold surprises in store. The other day it was my crash. Today Richie had an unfortunate puncture. It is always annoying to lose time that way, although, with everything that lies ahead of us, the time lost is very small.”
Contador dislocated his shoulder in a fall on the final sprint of stage six. “I still feel pain, but it’s healing,” said the Spaniard, who won the Giro in 2008 and was also triumphant in 2011, but was stripped of that title for testing positive for clenbuterol in the 2010 Tour de France.
Stage 11 today is a hilly 153-km leg from Forli to Imola, ending on the Enzo and Dino Ferrari racing car circuit that formerly hosted the San Marino Grand Prix.