LONDON (Reuters) - Serbia upset defending champions Hungary in a thrilling early water polo group match on Sunday, powering to a 14-10 victory and signaling to the Hungarians that they a have a huge battle on their hands to win a fourth consecutive Olympic gold medal.

In a match fought out with the intensity of a final, the two favorites matched each other goal-for-goal in the first half, before European champions Serbia took command with a prolific third-quarter performance.

The defeat ended water polo super power Hungary's unbeaten run of 17 games at the Olympics. They last lost a match 12 years ago in the group stages in Sydney.

The high-scoring match, full of the aggression and physicality for which the sport has been renowned since the 1956 "blood in the water" match, thrilled a stadium packed with 5,000 fans and each Hungarian goal prompted roars and chanting from a crowd awash with Hungarian flags.

The match was the first in Group B, the so-called "group of death" which features the top four-placed nations from the Beijing Games.

(Reporting by Sarah Young, editing by Ed Osmond)