Leon negotiated the various interruptions in a stop-start race to top the podium despite crossing the line in second after being caught out on the final restart.
However, he was promoted back to the top spot when second-placed Oliver Goethe was handed a five-second sanction for a safety car infringement on one of the numerous restarts.
But there could yet be a sting in the tail, with Leon himself subject to a post-race investigation for weaving.
Championship leader Luke Browning had been on to finish sixth and open up a gap at the top having entered the race level on points with Leonardo Fornaroli.
But a late incident left him in the gravel at Tosa, continuing his run of failing to score in a sprint race this season.
In a typically frenetic start, polesitter Kaper Sztuka was quickly thrust down the order and out of the podium places with Leon, Tim Tramnitz and sixth-placed starter Goethe all making ground.
But the action was quickly halted by a safety car intervention as Mari Boya’s Campos Racing entry spun into the gravel at the Variante Villeneuve midway through the first lap.
Oliver Goethe, Campos Racing
Photo by: Formula Motorsport Ltd
Following a short investigation, the stewards handed Tommy Smith a 10-second penalty for his part in the incident.
When the racing resumed, championship contender Leonardo Fornaroli got involved in a heated battle with AIX driver Nikita Bedrin over 13th, with the both drivers pushing the limits and sampling the plentiful gravel recently installed around the Imola layout.
No sooner had the racing resumed than it was halted once more, as Charlie Wurz assisted Callum Voisin into the barriers at Tosa, something that earned the Austrian a 10-second penalty.
And a third safety car intervention followed soon after, as Sami Meguetounif stuck the rear of one of the Prema car on the run to Tamburello and found himself stuck in the gravel.
Racing threatened to break out following a lap 11 restart but this was thwarted when Tasanapol Inthraphuvasak, who had started from the pitlane after failing to launch for the warm-up lap, pulled off the track at Rivazza.
Now on lap 15, Leon made his restart much earlier than before, catching out fourth-placed Sztuka who dropped three seconds off the lead trio and soon fell behind Dino Beganovic.
Championship leaded Browning had been set to finish sixth before he collided with Sztuka at Tosa.
On the last lap, the virtual safety car was deployed to cover the incident, with the pack freed to race the closing corners.
As the VSC was withdrawn, Goethe caught Leon napping and stole the lead with only two corners to go.
But his joy was short-lived after a five-second penalty for a safety car infringement on the previous restart demoted him back to second.
-
+4.600
4.6
+6.800
6.8
+7.900
7.9
+8.400
8.4
+9.000
9.0
+9.400
9.4
+9.900
9.9
+10.400
10.4
+10.800
10.8
+11.300
11.3
+12.000
12.0
+12.600
12.6
+13.600
13.6
+14.100
14.1
+15.100
15.1
+18.200
18.2
+18.500
18.5
+18.800
18.8
+19.200
19.2
+19.700
19.7
+20.300
20.3
+24.600
24.6
+30.500
30.5
+1 Lap
33.4
2 laps
6 laps
11 laps
14 laps
Source: Autosport