Tireless Inter Milan produced a rip-roaring home performance to overpower Barcelona 3-1 and leave the defending champion in real trouble after a thrilling first leg of their Champions League semi-final yesterday.

Barca lost by a two-goal margin for the first time under manager Pep Guardiola as strikes from Wesley Sneijder, Maicon and Diego Milito, after Pedro had given Barca the lead, set up a fascinating second leg at the Nou Camp next Wednesday.

Barcelona captain Carles Puyol was booked and will miss the rematch along with Inter midfielder Dejan Stankovic.

In one of the most electric atmospheres inside the San Siro in years, both sides stretched every last sinew to the limit in Europe's top club competition.

"Anything can happen in the second leg. We can go there and lose the game and lose the coach," Inter boss Jose Mourinho cryptically told a news conference.

"What happened today happened, it wasn't a dream. It was reality. We deserved to win. We saw a team working until the death. The team was destroyed by what they gave on the field."

Inter had the better of the early chances but first blood went to Barca, forced to make a 14-hour bus journey to reach the match because of the Icelandic volcano restricting flights.

Left back Maxwell, who quit Inter for the La Liga leaders last year, exposed his ex-teammates by setting up Pedro after 19 minutes.

The 22-year-old was again preferred to Thierry Henry in Barca's starting lineup and the diminutive spark-plug forward is quickly becoming a good bet to earn a spot on Spain's World Cup squad.

Inter, which has not won this competition since 1965 and is playing in its first Champions League semi-final since 2003, then demonstrated the steel-plated resilience Mourinho has instilled in his men by hitting back on the half-hour.

Argentine striker Milito, who missed two glorious chances from tight angles, turned his back on the goal when picking up the ball in the box but cleverly sent in former Real Madrid playmaker Sneijder for his score.

Goran Pandev did well early in the second half to release Milito in a barnstorming break and his cutback pass was scuffed home by right back Maicon, who was later taken off on a stretcher.

Milito headed in the third after 61 minutes and for a moment feared he had again been flagged offside before running to celebrate with the ecstatic Inter fans, who have been spoiled by four straight Serie A titles but starved of European success.

"I congratulate them but we'll see them next week," said Guardiola, whose side beat Inter 2-0 at home in the group stage.

"We are in the semi-final of the Champions League against a great team, it can happen. We move forward."

Guardiola was gracious in defeat and had only one complaint about the sticky San Siro pitch, saying the Nou Camp would be watered for the second leg.

"The pitch was not the one we wanted. At home we can choose, we have attackers who are very quick." He also refused to blame the long overland trip for his the defeat.

"I'm not a doctor so I can't say how much the journey affected us," he added.

Lionel Messi only had one good effort after largely being kept under wraps by the sheer brute force of Inter's defence.

Bayern Munich host Olympique Lyon in the second semi-final, first leg today.