David Warner has Sydney Thunder believing again

David Warner has helped the Sydney Thunder to believe again.

That's according to coach Trevor Bayliss as the Thunder's fairytale Big Bash League resurgence stretches into the finals.

A year ago, they were preparing for a post-mortem on the equal-worst season from any BBL team in a decade.

Not since the Thunder outfit of 2013/14 had a side won only one match in a BBL summer.

But led by new captain Warner, the lime green side surged to third place on the ladder this summer with a 5-3 record, easily securing a top-four spot and knockout date with the Melbourne Stars on Wednesday.

On the pitch, Warner scored the second-most runs of any player in the tournament, an unbeaten 88 against the ladder-leading Hobart Hurricanes the clear highlight of his first full BBL season to date.

The retired Test opener would likely have sat atop the batting rankings if not for rain; wet weather meant the Thunder played one fewer game than the Perth Scorchers, whose star allrounder Cooper Connolly scored only five more runs.

But Bayliss has noticed Warner's impact stretch beyond the playing field.

"The job he's done as captain, it's not just about his batting for example, it's his personality," he said.

"He's always up for it, he's a positive character. Loud, obnoxious sometimes, but the boys love it.

"I think it's the confidence that he gives his teammates, and their belief then that they're good enough to do the job.

"They're all good players, they sometimes just need that belief. Certainly I think the results have shown this year."

Public opinion of Warner has wavered dramatically over the years, from his early days as a hyper-confident ballstriker, to his role in the Newlands ball-tampering controversy, and the shift to introspection that followed.

The latest iteration of Warner has made an impression on new Thunder teammate Sam Billings.

"People have this perception around him, but he's incredible in terms of the conversations he has with individuals and the consistent drive," the Englishman said.

"You see why he's one of the best players in the world, still at the age of 38. I'm learning off him every day."

As they prepared to host a similarly resurgent Stars at ENGIE Stadium, Warner felt the Thunder still had room for improvement.

The team's largest partnership, 89 runs between Warner and Matthew Gilke against Perth, was only the 10th-largest of the regular season.

The side also does not have a wicket-taker in the top 10 for the tournament.

"The batters haven't all gelled together and gotten big partnerships," Warner said.

"We talk about bowling partnerships as well, one has leaked at one end and then the other has taken wickets.

"We still haven't played a complete game yet, which for me is scary."