The duo regularly practice together, for instance in Belgrade last week, and their knowledge of each other’s game was evident in a catalogue of cat and mouse rallies.
Ultimately an overheard error at 6-6 in the breaker cost world No.30 Krajinovic, prior to Djokovic lifting his level.
“First set, I think he was the better player. He was serving for the first set and I was lucky,” admitted Djokovic during his on-court interview.
“In the second set, I stepped it up, I played better and I am just pleased with the way I finished the match.
“We are good friends, we train together a lot and it is never easy to play someone that you are very close to. I try to be there as a friend, as a mentor. We go back a long way.”
One match left to equal Sampras
Standing in the way of the Serbian joining Sampras in the history books is world No.24 Borna Coric in their last 16 tussles.
The Croatian, who earned his second-round ticket 6-4, 6-4 against Taylor Fritz, hasn’t taken a set off Djokovic in their previous encounters, with the 17-time major winner holding a 3-0 head-to-head record.
Their most recent match was a straight sets triumph in the 2018 Shanghai Masters final.
Further into the draw and Djokovic is seeking his fifth piece of silverware for the season. Over on the other side of the draw is defending champion Dominic Thiem.
The top two seeds hit together earlier in the week in Vienna but can’t meet in competition until the trophy showdown.