Though the vast majority of the 100,000-strong crowd were baying for a Valentino Rossi victory, it wasn't to be the Italian's day; Jorge Lorenzo claimed a third win of the season, extending his championship lead on "The Doctor's" home turf.
Lorenzo's triumph was secured by just 0.019 seconds from rival Marc Marquez, who was helpless to stop his fellow Spaniard catching his slipstream and pipping him to the post.
Ducati rider Iannone, with a point to prove, fought hard with teammate Andrea Dovizioso -- eventually seizing third and breaking the fastest ever speed recorded by a MotoGP bike in the process, an eye-watering 354 km/h (220mph.)
The build-up to the race meeting alone was worthy of a novella. After Lorenzo's announcement that he was leaving Yamaha for Ducati next season, the paddock was waiting for the resulting merry-go-round to come to a stop.
In the event, Maverick Viñales confirmed his widely expected move from Suzuki to become Rossi's teammate.
Iannone, meanwhile, will make way for Lorenzo at Ducati, replacing Viñales at Suzuki.
The moves, announced as bikes were being wheeled off the team trucks at the Mugello circuit, added spice to a breathless qualifying session.
Right up to the death it looked as though Viñales would take pole, before a searing lap from Rossi pushed the veteran into first. The packed grandstands wrapped around this idyllic track erupted in delirious joy.
The main event
At first, the race too looked as though it had been authored by Rossi's personal scriptwriter. But things turned out differently and, as ever, the inevitable fly in the ointment seemed to be Lorenzo.
The world champion's Yamaha spat venomously from the second row of the grid, reaching the first corner in the lead.
Viñales, by contrast, had a disastrous start, and found himself down in 11th place after a problem with his bike's electronics.
Rossi, roared on by a partisan crowd, kept pace with Lorenzo -- the two bikes tearing through clouds of yellow smoke emanating from the home favorite's fans.
But smoke of a different kind signaled the end of the Italian's race.
On lap eight, it began to belch from his bike and, to the dismay of the majority present, Rossi pulled his Yamaha off the track.
When he eventually arrived back in the pits, hitching a ride on a scooter, he walked dejectedly into the team garage with his visor down.
The show goes on
Back on the track, Lorenzo was being pursued by another Rossi nemesis in Honda's Marquez.
The battle between the two Iberians was followed by an equally charged affair between the two Ducatis.
But Iannone bemoaned the time-sapping battle with his teammate: "We passed each other a couple of times and we lost a bit of time; after passing him however I no longer had any chance of catching the two up front."
And Dovizioso, whose luck has repeatedly deserted him this season, complained of a painful arm pump problem.
"Halfway through the race I had a problem with arm pump in my right arm and lost a lot of my strength," said Dovizioso. "This forced me to drop my pace, but above all it caused me to make a few errors."
With three laps remaining, Marquez attacked and briefly led.
Lorenzo fought back, retaking first, but on the last lap a daring pass from the younger man saw him lead into the final corner.
Incredibly, one final twist remained: Lorenzo caught onto Marquez's slipstream and beat him across the line, with just 0.019 seconds separating the two.
"I did the best race I could do today -- I really tried everything." Marquez sighed. "I took several risks in an attempt to win, but on the home straight Jorge slipstreamed me. Now we have to keep working on acceleration because we're still lacking a little in that regard."
An exhausted Lorenzo spoke of his disbelief at beating the Honda: "I tried to escape, pushing so much on the changes in direction and I used a lot of energy and I thought I maybe I didn't have enough to fight with Marc for the victory," he said after the race.
"He maybe saved more energy and was more powerful at the end, but my luck was the engine this time. Today, if I had been fighting with Rossi or Iannone, I wouldn't have won, it was a crazy battle."
While clearly devastated at missing out to a mechanical problem, Rossi was philosophical. "The positive thing is that I was competitive over the whole weekend and I was strong," he told reporters. "I could have fought for the victory."
Catalunya is up next. One of Rossi's favorite tracks, it is also a home race for Marquez. Expect more fireworks on and off the track.