"Little man wanted a selfie, I asked where is phone was, he said with his parents, so I asked where they were and he pointed across the arena, so I asked how he got way down here and he just pointed at his head", Ohanian tweeted.
"I think we can expect the same from Djokovic because he is in the same league as Roger and Rafa".
"It's going to be an exciting year".
Ostapenko, this year's surprise French Open victor, triumphed 6-2 3-6 10-5 in their exhibition contest at the Mubadala World Tennis Championships on Saturday, in what was the first meeting between the pair.
"It's too tough. I think everybody can look forward to a great and tense start of the season".
Williams' inconsistency on serve hurt her as she fell 0-5 behind in the deciding super tie-break, fighting back to 8-5 before the world number seven wrapped it up.
Ranked 22nd in the world, Williams would not need a wildcard to play in the first Grand Slam tournament of the new season. She gave birth to her first child, a girl named Alexis Olympia Ohanian Jr., on September 1.
Williams was very competitive despite losing to French Open champion Jelena Ostapenko
Another player in the field looking to build on his successful 2017 is South African Kevin Anderson.
The 30-year-old has not played a match since Wimbledon where he was forced to retire against Tomas Berdych with an elbow injury, which kept him on the sidelines for the following six months.
That tournament is set for January 15 through January 28 at Melbourne Park.
"I want this for sure but actually I felt really fine (physically) at the end of the (2017) season. So, it would be a good way to return for both these players", said Anderson. We all are eager to see what Novak is going to do when he comes back. "I have nothing to lose and I will just enjoy the match".
Serena Williams was "excited to be back" after completing her first match since giving birth fourth months ago.
Thiem, a two-time French Open semi-finalist, has been one of the standout players from the younger generation and has been able to challenge the so-called "Big Four" but he has a reputation of overplaying, and running out of steam towards the tail-end of the year.
Nadal and three-time major victor Stan Wawrinka were scheduled to take part but pulled out to allow further recuperation from respective knee problems.