Thiim managed to squeeze past Bamber at the beginning.
"There was the usual amount of bump and grind and associated carnage further down the grid, but fortunately the leaders all escaped that and, this time, there were no hold-ups on the yellow flags," said Tait.
No one in the top four was able to make a serious challenge to change position during the first half of the race, before Giermaziek and Thiim began to pull away from Bamber and a fight developed behind him for fourth.
"This left Earl pretty much on his own sitting, about 0.7 of a second behind second place ..." said Tait.
Bamber settled into a comfortable pace to maintain his position, with Giermaziak driving on for the win while Thiim, who did not race the first three rounds of the series, settled for runner-up.
Giermaziak extended his series lead by moving on to 96 points, but Bamber remains in contention on 87, with a bit of a break on Germany's Michael Ammermller, who sits on 64 points after coming fifth in the last four rounds.
There will now be a break before the next race at Circuit de Spa-Francorchamps in Belgium on August 24.