The Bentley Team HTP driver, who can still win the Blancpain Sprint Series drivers’ title as well as the overall Blancpain GT Series title, set the best lap of the day during the first practice of the day.
Buhk clocked the fastest time of 1:38.084 in his third lap around the Dutch circuit, 0.121s quicker than the fastest time set by the No. 2 Belgian Audi Club Team WRT Audi of Nicki Thiim.
The Dane, who will share his Audi R8 LMS ultra with Belgian driver Frederic Vervisch, was three tenths faster than Series leader Robin Frijns in the No. 1 Audi.
Fourth fastest on track was the No. 6 Phoenix Racing Audi of Markus Winkelhock and Niki Mayr-Melnhof (+0.553s).
Misano race winner and title candidate Norbert Siedler and his teammate Jeroen Bleekemolen only managed P6 (FP1) and P14 (FP2) in the No. 333 Rinaldi Racing Ferrari 458 Italia GT3.
Six Audi R8 LMS ultra cars in total made it into the top eight of FP2, with the two GT Russian Team Mercedes SLS AMG GT3 cars taking fifth and eighth place.
The second practice session was red-flagged twice, both as a result of the No. 71 GT Russian Team Mercedes ending up in the gravel trap.
On-track action resumes tomorrow with Qualifying at 10.15 am local time, followed by the Qualifying Race to be held at 2.15 pm.