The margin between winning and losing has shrunk to a single vote.

That is the finding of a late afternoon tally of county elections websites in the hotly contested state Senate primary between Democrats Juan Vargas and Mary Salas. Spending from outside interest groups topped $2.5 million in the contest.

After all that money, Salas, a San Diego assemblywoman, has 24,014 votes. Vargas, a former San Diego assemblyman, has 24,013. Vargas has been slowly picking up votes since election evening, when it appeared Salas was headed toward a narrow victory.

The margin had closed to 48 votes earlier this afternoon. It is not clear how many votes remain to be counted. A recount could be next.

— Shane Goldmacher in Sacramento