Loris Karius began his Besiktas career for real on Sunday night but was unable to help his new team-mates claim three points against Bursaspor.
The 25-year-old, who moved to Turkey on a two-year loan from Liverpool with a view to a permanent deal last month, made a strong one-on-one save in the first half.
But he will be very disappointed with his positioning for the equaliser which earned Bursaspor a 1-1 draw after Ryan Babel's opener.
As Yusuf Erdogan crossed from the left, Karius moved towards the ball but did not get close to it and he left a huge gap at his near post which Diafra Sakho exploited by poking an untidy volley into the net.
The Bursaspor leveller came in the 86th minute, shortly after Karius had received a yellow card for time-wasting.
Karius was not named in the Germany squad for the upcoming games against France and Peru, so he must now wait two weeks for his next chance to impress.
Besiktas host Malatyaspor on September 16, before beginning their Europa League group campaign against Sarpsborg four days later.