A winner at Dubai and gold medalist at the Olympics earlier this year, top seed Dementieva has not dropped a set this week and has lost just 12 games over her last three matches.
The 27-year-old is through to her fifth championship of the year and will be after her 11th title on Sunday when she faces fourth seed Caroline Wozniacki of Denmark.
Leading the WTA with 11 semi-final appearances this season, Dementieva needed just over an hour to dispose of the 18-year-old Cirstea, who claimed her maiden title earlier this month at Tashkent.
Dementieva, who converted all five break points she forced on Saturday, continued what has been an outstanding campaign.
A semi-finalist at Wimbledon and the US Open, she is on the verge of winning three titles in one season for the second time in her career, having accomplished that feat in 2003.
While she ousted one rising star in the semis, another awaits Dementieva in Sunday's final.
Wozniacki defeated sixth seed Li Na of China 7-6 (7/1) 3-6 6-2 to continue her breakthrough season.
The 18-year-old had not won a WTA singles title coming into 2008, but is now a victory away from claiming her fourth following victories in Stockholm, New Haven and Tokyo.
Wozniacki, ranked 16th, lost her only previous meeting with Dementieva during the Olympics.