Iannone, who confirmed on Thursday he will leave Suzuki at the end of the 2018 season, left it until the final 30 seconds of the 45-minute Friday morning session to move to the top of the times, posting a best lap of 1m47.253s.

That was 0.550s up on Pirro, making his first of three planned starts on a third factory Ducati this year, who led the timesheets for the bulk of the running and ended up second.

Andrea Dovizioso made it a Ducati 1-2 for most of the way with a lap 0.192s slower than Pirro, which proved good enough for third in the final reckoning, 0.708s down on former teammate Iannone.

Yamaha's Maverick Vinales crashed at the first corner, San Donato, on his very first flying lap, but was able to recover to set the fourth-quickest time, fractionally slower than Dovizioso.

Setting identical times were Pramac Ducati's Jack Miller and championship leader Marc Marquez on the best of the Hondas, both recording a 1m48.035s to take fifth and sixth places.

Rookie Franco Morbidelli (Marc VDS Honda) was an impressive seventh, less than two tenths shy of Marquez and 0.007s ahead of his mentor Valentino Rossi on the second works Yamaha.

Jorge Lorenzo (Ducati) was a further thousandth of a second behind in ninth, while Cal Crutchlow (LCR Honda) completed a top 10 split by a little under a second.

Danilo Petrucci, who is vying to replace Lorenzo at the factory Ducati team next year, had a subdued start to his home race weekend in 13th place, making him the slowest of the four GP18 riders.

Dani Pedrosa likewise endured a tough opening session on the second works Honda that left him 17th.

Thomas Luthi (Marc VDS Honda) was the only other crasher besides Vinales of a relatively incident-free session, losing the front end at the downhill Scarperia right-hander at the halfway point.

Practice results:

Pos.	#	Rider	Bike	Time	Gap
1	29	Andrea Iannone	Suzuki	1'47.253
2	51	Michele Pirro	Ducati	1'47.803	0.550
3	4	Andrea Dovizioso	Ducati	1'47.961	0.708
4	25	Maverick Viñales	Yamaha	1'47.995	0.742
5	43	Jack Miller	Ducati	1'48.035	0.782
6	93	Marc Marquez	Honda	1'48.035	0.782
7	21	Franco Morbidelli	Honda	1'48.211	0.958
8	46	Valentino Rossi	Yamaha	1'48.218	0.965
9	99	Jorge Lorenzo	Ducati	1'48.219	0.966
10	35	Cal Crutchlow	Honda	1'48.229	0.976
11	5	Johann Zarco	Yamaha	1'48.272	1.019
12	42	Alex Rins	Suzuki	1'48.274	1.021
13	9	Danilo Petrucci	Ducati	1'48.304	1.051
14	41	Aleix Espargaro	Aprilia	1'48.384	1.131
15	44	Pol Espargaro	KTM	1'48.570	1.317
16	17	Karel Abraham	Ducati	1'48.573	1.320
17	26	Dani Pedrosa	Honda	1'48.669	1.416
18	30	Takaaki Nakagami	Honda	1'48.878	1.625
19	19	Alvaro Bautista	Ducati	1'48.920	1.667
20	38	Bradley Smith	KTM	1'49.086	1.833
21	53	Tito Rabat	Ducati	1'49.181	1.928
22	12	Thomas Luthi	Honda	1'49.460	2.207
23	45	Scott Redding	Aprilia	1'49.499	2.246
24	55	Hafizh Syahrin	Yamaha	1'49.650	2.397
25	10	Xavier Simeon	Ducati	1'50.315	3.062