Serving for the title at 5-4 Sunday, Tsurenko lost 13 straight points.
Tsonga said he knew he had to attack during the tiebreak.
Tsonga will face Medvedev in Saturday's semifinal, who believes he's primed for a strong Australian Open after seeing off Milos Raonic in the quarterfinals.
That became 6-4 before Medvedev won the next four points to claim the set. Serving at 2-3 in set number two, Tsonga saved three break points with winners and he was a point away from breaking Alex twice in the next game, only to squander both opportunities after good serves from the home favorite.
Nishikori had the better of the second set but couldn't take advantage of eight break points.
The Ukrainian took an injury time out after rolling her ankle while being broken in the first game of the third set and was powerless to prevent the world number eight from storming to her 12th career title.
But the world No.16 nearly let the first set slip as Tsonga twice rallied from 0-40 down to hold serve and then shoot to a 4-1 lead in the tiebreaker.
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"Despite (the) many chances that he had, I managed to hold my serves so I'm happy about it and I'm happy about the win", he said.
"I'm happy to go into Melbourne, one of my favourite tournaments there", he said.
But he chalked it up as another valuable lesson against a red-hot opponent as he prepares for next week's Sydney International, where he made the final a year ago, and the Australian Open later this month.
"Great final today, I lost to him (Medvedev) previous year in the final in Japan, so I'm happy to get revenge today". He also beat three-time Grand Slam champion Andy Murray in the second round in Brisbane.
Second seed Nishikori had confirmed his place in the final earlier in the day when he required just 66 minutes to beat Jeremy Chardy.
"I like the way I played these two matches against great players".
"I've never had a week like this to start the season, so it gives me a lot of confidence".