Mr. Trump, who only won Georgia's 6th Congressional District by 1 point in November, called to congratulate Ms. Handel on her victory.
Winning the June 20 run-off will be a steeper challenge for Ossoff, however, as Handel will nearly certainly benefit from her party coalescing around a single candidate in a conservative-leaning district.
He benefited from a fractured Republican field of 11 candidates, some of whom emphasised their loyalty to Mr Trump while others kept their distance.
Still, it's unclear whether Ryan will improve Handel's chances - or make them worse.
"This election is about deciding the things that unite us are stronger than the things that divide us", Ossoff tweeted Monday. The district, which spans parts of Fulton, DeKalb and Cobb counties, has been in Republican hands since 1979 and was held for 20 years by former House Speaker Newt Gingrich.
A Georgia congressional election in a historically conservative district is headed to a runoff that raises the stakes in an early measure for President Donald Trump and both major parties ahead of the 2018 midterm elections. Simas says both Price and Culberson won their reelection campaigns easily.
He said Democrats were shocked into action by Trump's victory in November.
The 6th district encompasses much of suburban Atlanta and until recently was considered a shoe-in for Republicans.
A run-off would likely be close, and should Republicans regroup and coalesce strongly around their candidate they could keep the seat.
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The security deposit is forfeited if a candidate fails to garner a minimum of 1/6th of the total number of valid votes. The Congress, which was the main Opposition party in outgoing municipal councils, finished third with 29 wards.
As for whether Trump will campaign with Handel, Spicer said: "We'll see if we're needed".
While Handel can keep the district red, she's going to need a state party that can help with some of the financial and get-out-the-vote heavy lifting.
Ossoff is coming under fire for spending more than $8 million on television ads, The Washington Free Beacon reported.
The nearest Republican - former state secretary of state Karen Handel - came in at just 19.8 per cent.
The Ossoff political threat drew the personal interest of Trump, who recorded a robocall urging Republicans to troop to the polls and block the Democratic upstart.
Republicans, meanwhile, have made their own attempts at nationalizing the race. "It is now Hollywood vs. Georgia on June 20th", Trump wrote, alluding to celebrity donations that came in for Ossoff.
"They were clear going into this election, they said their goal was to get over 50 percent".
"BIG "R" win with runoff in Georgia. They forget about what the middle class people, the hard-working, the lower class - whatever you want to call them - want".