Jiri Lehecka celebrated his second ATP Tour-level title, but was disappointed it came about following the retirement of Reilly Opelka.

Lehecka was crowned champion of the Brisbane International on Sunday, after Opelka had to withdraw due to a back injury early in the first set.

Opelka, who defeated Novak Djokovic in the quarters, was trailing 4-1 at the time.

The American will now hope to regain fitness for the Australian Open, which starts on January 12.

"It is never easy to finish a match this way, I know how you feel Reilly," Lehecka said.

"It has been an honour to see you back playing and if your body can take it you will be there for many more years.

"It was a great week for me in Brisbane. I just love to play here in Australia. I want to thank everyone for coming to watch and my team."

Elsewhere, Kei Nishikori's first Tour-level final in six years ended in defeat as he went down 2-6 1-6 3-6 to Alexandre Muller at the Hong Kong Tennis Open.