Brisbane, Australia (SportsNetwork.com) - U.S. Open runner-up Kei Nishikori and former Brisbane finalist Grigor Dimitrov were among Wednesday's second- round winners at the Brisbane International tennis event.

The second-seeded Japanese star Nishikori got past American two-time NCAA singles champ Steve Johnson 6-4, 7-5.

"New year is starting, and obviously I'm playing much better these couple years," said Nishikori, who finished 2014 at a career-high No. 5 with 54 match wins.

"I have more confidence and I beat a lot of Top-10 guys [these past] two, three years. If I can play good tennis all the time, I think I have a lot of chance to go [to the] top level. Hopefully this is going to be a good start."

Meanwhile, the rising Bulgarian and 2013 Brisbane finalist Dimitrov saved two match points before coming from behind to beat France's Jeremy Chardy 3-6, 6-4, 7-6 (10-8) on the hardcourts at Queensland Tennis Centre.

An upset came when capable Slovak Martin Klizan saved six match points before taking out seventh-seeded 2012 Brisbane runner-up Alexandr Dolgopolov of Ukraine 1-6, 7-6 (8-6), 7-6 (9-7).

Klizan will face Dimitrov in the quarterfinals.

One other result saw Bernard Tomic handle wild card and fellow Aussie Thanasi Kokkinakis 7-6 (7-2), 6-1.

Tomic will battle Nishikori on Friday.

In some more second-round action on Thursday, top-seeded Roger Federer will meet Aussie wild card John Millman and third-seeded Canadian slugger Milos Raonic will take on Kazakhstan's Mikhail Kukushkin.

Federer lost to Aussie favorite Lleyton Hewitt in last year's all-former-No. 1 Brisbane final.

Brisbane serves as a tune-up for the Australian Open, which will begin January 19 in Melbourne.