When Vladimir Putin jumped into the ring to congratulate the winner of a bloody martial arts fight and was greeted with a cascade of boos from a large part of the 20,000-plus crowd, the experience seemed just this once to set him back on his heels, if only for a moment.

Throughout much of the world, politicians can expect to provoke the boo-birds when they show up at sports events, but Sunday evening’s bout — shown live on national television — was a first for Russia’s authoritarian prime minister. He recovered and managed to say his piece, but by Monday the Russian blogosphere was alight with arguments, put-downs, debunkings and catcalls.

Putin’s ruling United Russia party is heading into parliamentary elections in just two weeks, and though it is certain to win, its popularity has been sagging. A poor showing — or rumors of a poor showing, depending on the perceived reliability of the officially announced results — could open a chink in what has been up to now an impregnable fortress of power.

“The end of an era,” exulted Alexei Navalny, a crusading anti-corruption activist and blogger. Oh, please, replied Yaroslavl Zagorets, writing on lenta.ru: “It seems logical that among the 22 thousand people there were those who cannot stand politicians trying to score points.”

Still, the whole country had a chance to witness dissatisfaction with Putin, and this is the first time that has happened since the submarine Kursk sank in 2000, a national disaster that most believe Putin handled poorly and that appears to have persuaded him to crack down on independent television as a result.

Sunday’s fight was at the Olympic Stadium here, and it featured the Russian Fyodor Emelianenko, coming off a series of losses, against the ferociously tattooed American Jeff Monson. Mixed martial arts is called “fighting without rules” in Russian, and this bout lived up to the name. Monson, 40, was beaten bloody, and lost.

Suddenly Putin was in the ring. “Today all martial arts fans are having a feast,” he began, and then the boos began to descend. Putin stopped, resumed, spoke louder. “We are all grateful to Fyodor Emelianenko, a real Russian bogatyr” — a Russian knight of old — “and not just because he is very strong and has wonderful muscles but also for his character and will, a real Russian bogatyr. I am greeting you, Fedya.”

What happened would be nothing in, say, Philadelphia, where Eagles fans once booed Santa Claus and, more recently, Flyers fans booed Sarah Palin. President Harry Truman was booed at a Washington Senators game in 1951, and when baseball returned to Washington fans continued the tradition with raspberries for both President George W. Bush and President Obama. Gov. Rick Scott of Florida managed to get booed by baseball fans twice within the space of two weeks this year, at a Yankees spring training game and the Tampa Bay Rays home opener. In Miami on Sunday, Nascar fans seemed to be booing Michelle Obama and Jill Biden, who had come to show their support for veterans.

But Russia is different. Muscovites are not big fans of Putin or President Dmitry Medvedev, and when major streets are shut down for agonizingly long spells to allow their motorcades to pass, drivers in the capital have more and more taken to leaning on their horns in unmistakable protest. In the rest of the country, though, the Kremlin’s carefully maintained image has been unsullied by dissent, especially on television.

By Monday, Russian TV was — unsurprisingly — mum on the outbreak the night before. Tapes of the bout cut off the aftermath. (Leaders from other countries might shy away from a sport as violent and sensational as mixed martial arts, where each round here was announced by a model in a tight tank top and a bikini bottom, but Russians were thrilled with the victory and it is right up Putin’s alley.)

The TV blackout served to stoke even more criticism on the Internet, which is relatively free here. Putin’s allies fought back. A pro-Kremlin blogger, Elena Savva, argued that the booing and whistling was directed at the defeated Monson, “pathetic, beaten, hands trembling.” Others tried to argue that the crowd was cheering Putin, stretching out the first syllable of his last name much as Red Sox fans in happier days used to do with Kevin Youkilis. But whistling here is always derisive, and there was no explaining that away.