The Congressional District 2 showdown between Republican Martha McSally and Democrat Ron Barber has gone into overtime - and it could come down to instant replay.

McSally holds a minuscule lead of less than two-tenths of a percentage point over Barber - a 400-vote difference in a race in which more 228,000 votes have been tabulated, with several days of additional vote counting to go.

What remains are an estimated 70,000 votes in Pima County, about 27,000 of them provisional ballots that need to be verified and the rest early ballots that were dropped off at polling places or delivered in the late mail on Tuesday. There is also an unknown number of outstanding ballots in Cochise County.

Thus far, Barber holds about a 3-percentage-point edge among Pima County voters, while McSally has a 20-point advantage in the much smaller Cochise County, all of which portends a squeaker.

If the race gets any tighter, it's worth mentioning that a difference of 200 votes or fewer goes to recount under state law.

On Wednesday, both candidates vowed to wait patiently as election officials count the ballots and sort through the confusion that led to so many people having to cast provisional ballots at the polls.

McSally, 46, said at a morning press conference that she feels optimistic that her lead will hold up. While many are calling her showing a surprise, McSally said that's not how she views it.

"We've been telling people all along that this is going to be a very close race. … I felt like we were in a strong, steady place all along," said McSally, a retired Air Force colonel.

Barber, 66, didn't speak to reporters on Wednesday, but his campaign issued a statement highlighting the fact that the race is still too close to call and that Barber won decisively among early voters, which are the majority of the remaining ballots.

"We are cautiously optimistic about what the early ballots that were walked in will look like," said Jessica Floyd, Barber's campaign manager.

It has been a long year for both candidates, especially Barber.

This is Barber's fourth election of the year, having won the special primary and general elections to complete former Rep. Gabrielle Giffords' term. But almost as quickly as he took his seat in Congress, he had to hit the campaign trail again to try to win his own two-year term. He was unopposed in the Aug. 28 Democratic primary.

McSally ran in the April special Republican primary to try to replace Giffords but lost to Jesse Kelly, who then lost to Barber. She easily won the regular Republican primary for the right to take on Barber and, as she says, complete her transition from a career in the Air Force to Congress.

The McSally-Barber showdown is one of two Arizona congressional races that remain undecided.

In District 9, former Democratic state lawmaker Kyrsten Sinema leads former Paradise Valley Mayor Vernon Parker, a Republican, by less than 2 points. The district is in the metro Phoenix area, where Maricopa County election officials report about 400,000 ballots remain uncounted.

A number of other races of interest statewide, and in Southern Arizona, remain too close to call with so many ballots still uncounted. They include:

• Proposition 118, which would stabilize annual payouts to schools from the state land trust so districts can better plan for how much money they will receive, was a virtual dead heat at the end of the day on Wednesday, with 49.9 voting yes and 50.1 saying no.

• Legislative District 10 House, where Democrat Stefanie Mach held a 1 point, or about 1,100 vote, advantage over incumbent Republican Ted Vogt for the district's second seat.

Incumbent Democrat Bruce Wheeler is assured of winning the other seat.