SSR Performance driver Bortolotti was unable to take the start in the second race of the weekend after the technical issue that first appeared in qualifying couldn't be fixed in time for the formation lap.
But having dominated Saturday's opening contest to score his first DTM win, the Italian driver was well versed with the conditions at the Nurburgring, and he put his knowledge to good use to help Lamborghini claim a double win on the home turf of its German rivals.
Standing in the garage of Grasser Racing, the outfit with which he competed in the DTM last season, Bortolotti advised the crew to increase the tyre pressure at the next pitstop in anticipation of more rain.
"Mirko was standing next to me and said: 'Boss, we have to drive at high pressure,'" Grasser boss Gottfried Grasser told Motorsport.com's sister site Motorsport-Total.com. "I said: 'Rather not.'
"He was then like 'Boss, we'll do that, high pressure works!' I then put high pressure on his recommendation."
The call proved to be a masterstroke as Paul, who had been no match to race leader Lucas Auer in the first stint, was suddenly the quickest driver in the field after the pitstop phase.
Competing in only his first race weekend after being drafted in as a last-minute replacement for Mick Wishofer, Paul rapidly closed in on the Winward Mercedes of Auer with a fresh set of wet Pirellis and finally completed a move at the hairpin after duelling for several laps.
Once in clean air, Paul was able to pull away from the chasing pack, becoming the eighth different driver to win a race this season.
It also made Grasser a race-winning team in the DTM, the outfit having come close to the result a number of occasions last year - ironically with Bortolotti - but always falling short of making a breakthrough.
The Winward Mercedes team went in the opposite direction on tyre pressures to Grasser and that led to Auer dropping to third at the finish behind Porsche's Laurinch Heinrich, confirming Bortolotti's hunch was correct.
Winward team boss Christian Hohenadel told Motorsport-Total.com: "We had been too low with the air pressure. In addition, we needed some time with the Mercedes to bring the tyres to the right temperature."
The Grasser team was also spot on with tyre pressures at the beginning of the race, when only a small part of the track was wet.
This enabled Paul to jump from 13th on the grid to seventh in the first two laps, and move up to second after rain hit the track and turned the race into a contest of who can best manage their tyres in full wet conditions.
"We started with a tyre pressure that was actually not normal, it was that low," Gottfried Grasser said. "We knew: the rain tyre is at its limit. If you use it, you have to drive with low pressure so you can survive it until the stop.
"We thought we were totally wrong because there was a lot more water than expected. You usually can't do anything there with low pressure, but it worked.
"The rest was Max - with his incredible skill. Even with professional drivers, you sometimes see a sector off in these conditions. But with him, everything fit perfectly."
Both Auer and Paul pitted at the same time under a FCY, with Auer running several seconds ahead at this stage, but the Grasser driver was able to chase him down and take an unlikely win.
"When I was able to catch up to Lucas after the stop, I believed for the first time that I could win," said Paul. "He was very fair and didn't push me away like other drivers do. I really enjoyed it,"
Paul was added to the Grasser line-up on a one-off basis at the Nurburgring and it remains unclear who will occupy the seat next to Clemens Schmid, although Wishofer could make a return for the remaining four rounds.
