Simonds win means the House is evenly split 50-50 between Democrats and Republicans.
Yancey had won the 94th District by just 10 votes in November.
In the case of a tie in a House race, state law says the victor is chosen by lot - essentially, a coin toss.
The caucus vote comes after a day after Democrats appear to have secured a 50-50 tie in the lower chamber with a one-vote election victory after a recount in a Newport News House district. But on Wednesday morning Yancey's campaign asked the court to accept a ballot that had been tossed aside as an overvote.
Virginia law says that in the event of a tie, the election board will determine the victor "by lot", after which point Republicans believe the loser can petition for another recount; however, there is some disagreement among Virginia election experts as to how the law should be applied in this case.
While that agreement, coupled with Democrats as governor and lieutenant governor, could allow the party to pass a more progressive agenda on health care and other issues, Republicans still hold a slim 21-20 majority in the Virginia State Senate. David Yancey's 11,607, prompted renewed discussion about a rare power-sharing agreement that would need to be forged between the two parties in the coming weeks.
"One Republican official, and a recount observer, believed at the time the ballot was a clear vote for Delegate David Yancey".
But five hours and much nailbiting later, after painstaking counting overseen by local elections officials and the clerk of court, Yancey's lead narrowed before it gradually disappeared and then reversed, allowing Simonds to beat him by one vote.
The Dec. 19 recount, which left Simonds with 11,608 votes compared to incumbent Del. A three-judge panel still must certify the results, an event scheduled for Wednesday. When the process was complete, Simonds wound up ahead with 11,608 votes to Yancey's 11,607.
As she waited with her sister and daughter outside the building where the recount was conducted, Simonds said she wasn't going to celebrate until she had confirmation from the city registrar.
Last week, Republican Delegate Tim Hugo held on to his seat in Fairfax County after a recount made little change to his 100-plus vote lead. "There weren't any ballots going to the judges", Simonds said, adding with a laugh: "You can call me landslide Shelly as long as you call me delegate".
Simonds, who appeared on national television as recently as Wednesday morning as the surprise victor of a tense recount that reset state politics, could not immediately be reached for comment.
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