For days Democratic 16th Assembly District candidate Rebecca Bauer-Kahan has been a stalking horse, steadily gaining on Assemblymember Catharine Baker in this unexpected upset in the making. On Friday, Bauer-Kahan made a potentially decisive late move to the finish line.

With the number of uncounted ballots dwindling, a highly anticipated update by the Contra Costa County Registrar of Voters Friday shows Bauer-Kahan with a 2,170-vote lead over Baker, a two-term assemblymember, who is the East Bay’s lone Republican representative in the state legislature.

Bauer-Kahan’s campaign and Democratic Party officials in both Contra Costa and Alameda Counties expected the update would significantly build on a growing sense that Baker’s days in the assembly could be numbered.

Friday’s update in Contra Costa County was the first issued since Nov. 9. Previous results had shown Bauer-Kahan with a slight advantage. Baker, meanwhile, led in the Alameda County portion. The latest update shows Bauer-Kahan outpacing the percentage of voters in Contra Costa County from a week ago. She captured 54 percent of the latest batch of ballots to Baker’s 46 percent.

A daily update of new results posted by the Alameda County Registrar of Voters has shown a clear trend toward Bauer-Kahan since last Saturday. Before today, Baker’s lead had shrunk to just 159 votes. Alameda County is expected to post an update Friday afternoon.