Zumerle triumphed ahead of Paolo Necchi and Sergio Rota to re-open the title race after the black flag was shown to Swede Peter Sundberg.
The rolling start went off smoothly but Sundberg jumped the green light and crossed the line too far ahead of the pack for the race officials not to notice. With Maddalena and La Mazza having to pull out, the end of lap 1 saw Sundberg leading from Necchi, Zumerle, Ardagna Perez, Petrini, Piancastelli, Rota, Maggi, Smurra, Simoncini, Bellin and Moncada.
Zumerle was in good form as he showed when he attacked and overtook Necchi who, in turn, had to fight off an aggressive Ardagna Perez.
In the meantime the race officials decided to hit Sundberg with a drive through for jumping the start, just as Zumerle was setting the fastest lap as he pushed hard to close the gap on the Swede. Things were hotting up behind the front two with Petrini, Smurra and Maggi careering around the curves.
One of the quickest on the track was Nicolò Piancastelli. After nicking in front of Rota at the start, he posted the fastest lap so far of 2:12.194 as he wound up for an attack on Necchi, now down another spot after being overtaken by Ardagna Perez.
It was precisely during this stint that Piancastelli overshot turn one and accidentally clipped Ardagna Perez, who spun off the track. The Venezuelan had already been involved in two unlucky incidents - at Monza and at Zolder - but came back in eleventh position. Unfortunately for Piancastelli, there was no way back.
On lap five with Sundberg continuing despite his drive-through penalty, Zumerle was making his presence felt by flashing his lights. The gap between the two was only eight tenths with the others further back: Paolo Necchi (4.8 seconds down), Sergio Rota (6.2 down), Emanuele Smurra (10.7 down), Francesco Maggi (11.9 down) and Mauro Simoncini (14.1 down), in what was his 520th race.
The shock came on lap seven when Sundberg was shown the black flag for not coming in for his drive through. At the end of the race, one of the Trofeo's most respected and respectful drivers stated that he had not seen the officials' signal.
The episode opened the door for Pietro Zumerle and he wasted no time in extending the gap over the pack. There were a few tight duels taking place like the one between ex-team mates Petrini and Moncada. Moncada, starting from the back, made a remarkable comeback that, unluckily, ended when he clashed with Petrini and spun. The officials immediately hit Moncada with a drive through.
By lap ten, Zumerle led Necchi by 2.9 seconds, Rota (7.2), Smurra (9.5), Maggi (17.9), Simoncini (26.3) and Ardagna Perez (26.3) who, had recovered well from his spin and even overtook Simoncini.
Also going at it were Andreas Segler and Tiziano Frazza. The German managed to get past the Italian but then spun.
Up front Smurra was setting a series of quick laps that saw him glide into Sergio Rota's slipstream. Still, the tussle for third was far from exciting with the Bergamo driver closing the door in Smurra's face whenever he threatened to attack.
Not much happened from then on until the chequered flag with Zumerle winning from Necchi, Rota, Smurra, Maggi, Ardagna and Simoncini.
So, with Sundberg coming away with his points bag empty, Zumerle, Necchi and Rota have re-opened the championship race and reduced the gap to the leader.
He added race 2 to this morning's win and pocketed the fastest lap time for good measure.
It was another event-free rolling start in Race 2 but this time with the pack bunched was much closer together. Rota was slow out of the blocks and was overtaken by Necchi while Zumerle was attempting to create some space for himself up front and, from fourth, Piancastelli had slipped down to eleventh.
The second place held by the MotorMedia director lasted only a lap before he was overtaken by Rota and then Ardagna Perez. Moncada was out to make up for Race 1 and was soon involved in a fight with a Goldstein who had done well to climb through the field. After trying a few times, the Italian finally nudged past the series leader.
Most of the early action was going on at the front of the pack with Emanuele Smurra gunning for his first pole of the season. The ex-Trofeo champion turned up the heat on Necchi and overtook him on lap 5. His next target was Ardagna Perez, who was dealt with a lap later.
The Venezuelan slowed his tempo for a few seconds and allowed Necchi to pull back up to his bumper just as Rota was closing in on Zumerle.
Race 2 had a turning point of its own when La Mazza was too hasty in trying to edge past Goldstein at turn 6, clipping him and sending him into the sand. For the Panamanian, retirement was the only option as was La Mazza's drive through.
Up front, Rota had managed to scrape past Zumerle at the start of the main straight as he made the most of Zumerle straying wide in a curve.
Halfway down the field, Moncada and Piancastelli were taking each other on and the Trofeo's youngest driver also eased past Simoncini.
The episode that decided the race came on lap thirteen: with Zumerle hounding him, Rota locked his left front wheel and overshot turn 3. Even though he finished up in the sand, the driver from Bergamo made it back into the race in eighth.
Events up front influenced Necchi and saw him pressure Ardagna for third on lap fourteen. One lap later it was Moncada and Piancastelli drawing all the attention when they came together. Race officials ruled that the incident could have been avoided and slapped Piancastelli, who caused the spin, with a drive through that was later converted into a 25 second penalty.
Towards the end, with Zumerle fending off Smurra and Necchi having built a decent lead over Ardagna Perez, it was Sergio Rota trying to mount a comeback that saw him earn sixth spot after overtaking Simoncini.
The chequered flag soon marked a second win for Pietro Zumerle. A convincing Emanuele Smurra came second (for his first podium of the season) with Paolo Necchi in third.
Goldstein's exit, together with Sundberg's disqualification from Race 1, sees a much more open championship. The Panamanian-Swedish duo still lead but by just a point from Zumerle. Smurra is 14 points down, Necchi 15 and Rota 16.
The next Trofeo Maserati GranTurismo MC race will be at Oschersleben, on 4-5 September.