The former All Blacks great scored 21 points as the Kobe Steelers beat Jake White’s Toyota Verblitz in a semifinal on Saturday.
Carter crossed for a try and kicked four penalties and two conversions to steer the Steelers to their first playoff final.
The Kyodo News reported Carter also set up a try for Kiwi compatriot Fraser Anderson with a deft stab kick off the outside of his boot.
Kobe – who have former All Blacks coach Wayne Smith as director of rugby – won the inaugural 2003-04 Top League title when the competition was decided on a round robin basis.
Highlanders utility Richard Buckman started at fullback for Kobe, who will meet Giteau’s Suntory Sungoliath in next Saturday’s grand final.
Suntory needed a Giteau penalty to beat Yamaha Jubilo 28-25 in a golden point extra-time cliffhanger.
The former Wallaby landed a 42m goal in the fifth minute of extra-time after earlier helping create two tries for hat-trick hero Seiya Ozaki.
Giteau kicked 13 points to give defending champions Suntory a shot at a sixth title.
“We only got told it would be golden point when we were in the huddle [before extra time started],” Suntory’s former Highlanders lock Joe Wheeler told Kyodo News.
The Suntory side backed Giteau to get the job done.
“I knew he’d kick it,” Suntory’s Auckland-born Japanese test flanker Hendrik Tui told Kyodo News. “He’s always staying on and kicking at training.”
Carter and Giteau – both 36 – have been rivals since 2003 when Carter made his All Blacks debut, 12 months after Giteau’s Wallabies bow.
Both are winding their careers in Japan after stints in France – Carter with Racing 92 and Giteau at Toulon.
Carter is in his first season with Kobe.
Giteau joined Suntory last season and helped them win the 2017 Japan title.