The county GOP chairman had been in rough political water just three months before. He'd decided not to seek a second term as head of the state Republican Party, which had lost a 40-year-old State Senate majority on his watch.
The wins in Nassau boosted Mondello and cemented his reputation as a regional political giant, observers said.
"If American politics were the stock market, Joe Mondello's stock would be the hottest in either the Republican or Democratic parties," said Robert Zimmerman, a Democratic national committeeman from Great Neck.
But questions about a cool relationship with new County Executive Ed Mangano, a dark horse candidate turned spoiler, have complicated Mondello's comeback tale.
Lawrence Levy, director of the National Center for Suburban Studies at Hofstra University, noted the perception of strain between the two men because Mondello's GOP organization donated to Mangano only late in the race.
When Mangano began his campaign, he was surrounded by a close circle of supporters, Levy said, some of whom were not Nassau GOP loyalists. Still, Mondello's organization delivered for Mangano in getting out the vote at election time, he said, leaving him in the party's debt.
Levy summed up the dynamic this way: "While Mangano doesn't owe Mondello a lot, he can't run over him."
Mondello said murmurs about distance between himself and Mangano are false and the work of "naysayers" who know nothing about the relationship. Mangano, Mondello said, views him as "an older brother or maybe even a father."
His decision not to seek another term was partly a response to unrest upstate, according to party officials who requested anonymity. County leaders there had grumbled to each other about Mondello's absence from the region in terms of helping to raise money and recruit candidates.
In his nearly three years as state party chairman, the party raised about $4 million, according to the New York Public Interest Research Group. Prior to Mondello's tenure, it took in nearly $10 million over a comparable period.
Mondello said he served without a GOP governor and with a weak hold on the Senate, plus he confronted the Obama phenomenon - all of which diminished the party's sway and ability to raise funds.
So Mondello said he walked away to focus on Nassau, where he saw frustrated voters and an opportunity to strike.
With Mondello's blessing, Mangano emerged in May as the party's choice to take on Democratic incumbent Thomas Suozzi, who is now a consultant for Cablevision, which owns Newsday. Few gave Mangano a shot.
The Nassau GOP donated $18,200 to Mangano on Sept. 16. Between Oct. 8 and 21, two weeks before Election Day, the party donated $244,000. By the time the money rolled in, GOP-commissioned polls showed Mangano might actually win.
Mondello insists he was a believer from the start, and his strategy all along was to conserve funds for TV ads at the end of the campaign.
For his part, Mangano has said Mondello was involved and a valuable source of support from the beginning. He's dismissed speculation about ill will or a desire to see Mondello out as chairman.
At a recent Mondello fundraiser, Mangano gave credit.
"In the final stretch," he told the crowd, "when we needed a push, Mondello gave us the help."
Mondello said that regardless of the "liars" who want to sow discord between the men, a political reality is at work: Mangano must be on good terms with the Nassau GOP if he dreams of a political future.
If he ever gets the "cold shoulder" from Mangano, Mondello said he's the type that can forgive - but he will not forget.
"And when the time comes, I'm not going to be your best friend," Mondello said. "That's just the way it works."
With Celeste Hadrick
and James T. Madore