James, 29, has also netted three times in his first four matches for Everton in the Premier League following his summer move from Real Madrid.
The visitors from Poprad did not put on an offensive show either, but scored twice, which was sufficient for earning their first victory of the season.
Xinjiang began to take charge of the game back from the locker room on the way to a 19-point advantage after the third quarter.
Wuhan got rolling midway through the first quarter, going on a 9-0 run to move ahead and setting up a 23-12 advantage as the quarter time ran out.
The "Eisernen" made a perfect start on home soil as Christopher Lenz tested Mainz goalkeeper Robin Zentner in the early stages, before Max Kruse nodded home his debut goal after Sheraldo Becker's pinpoint cross to the far post in the 13th minute.
"This was to say the least, one of my most difficult races. The altitude took a toll on me and it simply took away my breath. I just can't remember much of the race. I am happy to win in such conditions in my personal best time. I just say it was a solid performance and I am happy to wrap up my season with a win. I will take two weeks break before starting my winter preparations," said Awuah.
"We are not a strong team, but we have shown our mentality and fighting spirit to make games more appealing, which is beneficial to the league," she said. Enditem
"To be honest I was over the limit today. At the end I gave everything that I had out there, it was an amazing match," the 27-year-old added.
The 51-year-old coach replaced interim coach Majid Namjoo Motlagh on the Tehran-based team.
New arrival Pedro Rodriguez scored the winner after the break as the Spaniard unleashed a missile into the net with both power and precision.
With the result, Union Berlin move up to third place in the standings, while Mainz stay 17th after suffering their third straight defeat of the new season.