MELBOURNE (Reuters) - Jerzy Janowicz, it is fair to say, has failed to live up to his billing since reaching the Wimbledon semi-finals in 2013.
The giant Pole with a howitzer first serve and one of the best forehands in the game has too often been let down by a fragile temperament when the going gets tough.
There are signs that he is maturing though.
On Thursday he kept his cool in the Melbourne heat to beat Frenchman Gael Monfils in five explosive sets to reach the third round of the Australian Open.
There were still signs of frailty, like when he caved in during the second set, losing it 6-1 after outplaying 17th seed Monfils in the first 6-4.
Crucially, however, when he lost a high-quality third set on a tiebreak, rather than implode like he has been known to in the past, the 24-year-old hit back with some stunning tennis to win 6-4 1-6 6-7(3) 6-3 6-3.
"I'm very happy, it means a lot for me," 44th ranked Janowicz, who gave Andy Murray a scare in the Wimbledon semi in 2013, told reporters.
"I've had a lot of problems in my career but I've always tried to practice hard in the bad moments and this was the first pre-season I could practice for one and a half months.
"Usually I have some problem with my body, and some personal problems, so today was a present for all that fight."
Janowicz, whose average first serve speed was 197kph but was out-aced 21-14 by Monfils, showed that his game was far more than just raw power.
He defended brilliantly at times and showed a sublime touch with many drop-shots that not even the elastic-limbed Frenchman Monfils could reach.
But it was his mental fortitude that really stood out as the former world number 14 set up a third round against Spain's Feliciano Lopez.
"I've been doing a lot of work on fitness. But I also changed my head," he said. "Even when I'm angry I fight for every single ball. I lost the tie break but was still fighting and deep down I knew that I could still win this match.
"It was a huge match for me."