Konta has reached this week her first semifinal since Wimbledon a year ago, having not won three matches in a row since then excluding Fed Cup zonal play.
Johanna Konta finished as the runner-up at Nottingham's Nature Valley Open for the second year running, but not before a controversial conclusion in which she lost her temper at a couple of dubious line calls and berated the chair umpire.
Barty opened with a love hold and quickly went a break up, but Osaka enclosed the best of her reflexes in return to break back in the fifth game, soon leveling from 0-3 to 3-3.
'It's an absolute joke, ' she complained.
Barty broke third-seeded Osaka three times and didn't face a break point in serve.
1 had battled back from a set down against the Australian before clawing her way back into the final set from 4-1 down to 4-4.
The British No.1 won only one more point as Barty clinched victory with a backhand pass. You're making decisions that affect our lives. "Do you fully understand that?" after a line call failed to go her way - losing focus and leaving Barty with the opening that she needed.
It was Barty's first tournament triumph of the year, the second of her career and a demonstration from the former junior Wimbledon champion that she could now even be an outside threat for the senior title at the grasscourt grand slam.
Top seed Barty will search for her first singles trophy of the season on Sunday night (AEST) - weather permitting. She was able to get the better of Kurumi Nara, Heather Watson and Dalila Jakupović on her way to setting up this semi-final encounter.
The world No.22, who beat Barty in the quarters previous year before losing to Vekic in the final, breezed through the opening set.
"I knew that Jo was going to be the toughest test this week, so I'm just really glad that I came through that and it was a really high quality match".
Vekić got the better of Konta in the final of this tournament previous year as she won 2-6, 7-6, 7-5 in a scintillating encounter.