It was the best qualifying showing so far from the three-time DTM champion on his return to the series, having sat out the 2021 season, with Abt Audi driver Rast beating Team Rosberg Audi rival Nico Muller to pole by 0.188s.
Thomas Preining completed the top three in his best DTM showing to date in the Team Bernhard Porsche, as Clemens Schmid was shuffled back from first to fourth in the final seconds of a frenetic qualifying.
After Ricardo Feller set the early benchmark time with a 1m41.323s, team-mate Rast quickly asserted control of the session with a 1m40.687s followed by a 1m40.221s that third Abt driver Kelvin van der Linde came closest to matching with an effort that was 0.127s slower.
Schmid, who suffered a right-rear tyre blowout entering Tamburello in FP1 on Friday, was the best-placed of the Grasser Racing Lamborghini quartet in third at this point as team leader Mirko Bortolotti elected to remain in the garage until there were just six minutes remaining of the session.
But it was Schmid who stepped up to lead Lamborghini's charge with a 1m40.198s to snatch provisional pole, Bortolotti going 0.059s slower.
However Rast then reclaimed the top spot with the only sub-1m40s lap of the session at 1m39.817s, with Muller and Preining also beating Schmid's time.
Another late effort from Feller split the two Grasser cars, leaving Bortolotti sixth-quickest, although the Italian will drop 10 places on the grid for running an incorrect set of tyres during FP2 that his team explained was caused by having the wrong tyre barcodes.
After a quick spin at Variante Alta, Kelvin van der Linde set the fastest middle sector of anybody on his final lap but it was good enough only for the seventh-quickest time.
But thanks to Bortolotti's penalty, he will start sixth, with double DTM champion Marco Wittmann the best of the BMW M4s starting seventh in his Walkenhorst Motorsport example.
Championship leader Sheldon van der Linde will carry 25kg from eighth on the grid in race one, after his victory last time out at the Lausitzring, with Mercedes drivers Lucas Auer (Winward) and Maro Engel (GruppeM) completing the top 10.
DTM Imola Qualifying results:
|1||René Rast||Audi R8 LMS Evo II||1'39.817|
|2||Nico Müller||Audi R8 LMS Evo II||1'40.005||0.188|
|3||Thomas Preining||Porsche 911 GT3 R||1'40.039||0.222|
|4||Clemens Schmid||Lamborghini Huracán GT3 Evo||1'40.121||0.304|
|5||Ricardo Feller||Audi R8 LMS Evo II||1'40.137||0.320|
|6||Mirko Bortolotti||Lamborghini Huracán GT3 Evo||1'40.180||0.363|
|7||Kelvin van der Linde||Audi R8 LMS Evo II||1'40.348||0.531|
|8||Marco Wittmann||BMW M4 GT3||1'40.409||0.592|
|9||Sheldon Van Der Linde||BMW M4 GT3||1'40.431||0.614|
|10||Lucas Auer||Mercedes-AMG GT3 Evo||1'40.474||0.657|
|11||Maro Engel||Mercedes-AMG GT3 Evo||1'40.570||0.753|
|12||Dennis Olsen||Porsche 911 GT3 R||1'40.597||0.780|
|13||Nick Cassidy||Ferrari 488 GT3 Evo 2020||1'40.626||0.809|
|14||Rolf Ineichen||Lamborghini Huracán GT3 Evo||1'40.631||0.814|
|15||Luca Stolz||Mercedes-AMG GT3 Evo||1'40.661||0.844|
|16||Laurens Vanthoor||Porsche 911 GT3 R||1'40.787||0.970|
|17||Philipp Eng||BMW M4 GT3||1'40.800||0.983|
|18||Timo Glock||BMW M4 GT3||1'40.927||1.110|
|19||Arjun Maini||Mercedes-AMG GT3 Evo||1'40.935||1.118|
|20||Maximilian Götz||Mercedes-AMG GT3 Evo||1'40.958||1.141|
|21||Marius Zug||Audi R8 LMS Evo II||1'41.063||1.246|
|22||Mikael Grenier||Mercedes-AMG GT3 Evo||1'41.127||1.310|
|23||Maximilian Buhk||Mercedes-AMG GT3 Evo||1'41.301||1.484|
|24||Felipe Fraga||Ferrari 488 GT3 Evo 2020||1'41.310||1.493|
|25||David Schumacher||Mercedes-AMG GT3 Evo||1'41.392||1.575|
|26||Dev Gore||Audi R8 LMS Evo II||1'41.396||1.579|
|27||Esteban Muth||BMW M4 GT3||1'41.397||1.580|
|28||Alessio Deledda||Lamborghini Huracán GT3 Evo||1'42.065||2.248|
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