After starting from his first pole position in over a year, the 25-year-old German led the race more or less from start to finish, only being headed when he made his two mandatory pit-stops.
It was more than enough to see the Abt-Audi driver come home 6.217 seconds clear of Bruno Spengler after the AMG Mercedes driver had passed Tom Kristensen's Abt car early on.
Swede Mattias Ekstrom was a fantastic third after working his way up from tenth on the grid by virtue of an inspired strategy that saw him make his fuel stop almost within sight of the flag.
Tomczyk on pole
The 2004 champion maintained his series lead but is now only four points ahead of team-mate Tomczyk with two races to go.
Fourth was Timo Scheider as the Abt team took three of the top four places, while Britain's Jamie Green was fifth for AMG Mercedes, although he would have been higher had Audi tactics not conspired to have Scheider block him while Ekstrom closed in at mid-distance.
Sixth was another Brit Paul di Resta, in his two-year-old Persson Mercedes, a result that kept him fifth in the championship and makes him the lowest-placed driver that can still win the title.
Defending champion Bernd Schneider put his AMG car seventh at the flag while Kristensen dropped to eighth ahead of Alex Premat and Mika Hakkinen.
British duo Gary Paffett - the 2005 champion - and Susie Stoddart, came home 12th and 18th in their one and two year old Mercedes' respectively.