To the outside world, Sens. Mitch McConnell and Rand Paul seem to be caricatures of two conflicting brands of Republicanism: a seasoned establishment veteran and a fiery tea party upstart. But the two Kentucky Republicans are trying to make the tension work for them.

In a deepening relationship that began last October on a NASCAR-coach-turned-campaign bus in Paducah, Ky., McConnell and Paul have come to realize that the same characteristics that make them so different also make them politically invaluable to each another.

Though few would call them friends, McConnell needs a tea party ally who can help him with a constituency he’ll need for re-election in 2014 as well as with an important faction of his Conference. And Paul needs an establishment adviser and someone who can translate his vision into a legislative record.

On the mid-October morning of Paul’s final debate in Paducah, McConnell showed up virtually unannounced with his staff. He wanted to spend the morning with the man who would be his next colleague, a man he didn’t know. After all, McConnell had thrown his support behind Paul’s primary opponent, Trey Grayson, a seasoned Kentucky politician whom McConnell had known for years.

But McConnell’s horse didn’t win the primary, and by October, Paul was in the middle of a campaign bus tour. McConnell hopped aboard and stayed the whole day, asking questions about the Kentuckians showing up to Paul rallies as well as about tea party politics.

“As the race unfolded, and you’ve seen an extension of this as they’ve grown to know each other better in the Senate, it became clear that you have a guy in Rand Paul who’s extremely curious, bright and has unique vision on policy — the art of politics — and you have a guy in Mitch McConnell who’s extremely good at the science — the politics, the process,” said Trygve Olson, a campaign consultant who served as the National Republican Senatorial Committee’s liaison to Paul’s campaign.

Olson added, “It was clear to McConnell after Trey Grayson had lost that Rand Paul had tapped into something that he needed to understand, and it was clear to Rand Paul that he needed to understand the science better in order to succeed.”

The relationship between the two Kentuckians isn’t always easy, but it’s one McConnell has been deliberate in cultivating, sources say, because of past problems with others in the state’s delegation .

“One of the things Mitch told me when I was running was that he had observed that the worst relationships in the Senate were often between Members of the same party from the same state,” Grayson said in an interview. “He wanted us to have a great relationship, to talk to each other, to work together.”

McConnell had an icy relationship with Paul’s predecessor, Hall of Fame pitcher-turned-Senator Jim Bunning (R). It was widely reported that McConnell, a master political operator, had discouraged campaign contributions to Bunning, which forced him to retire.

But the same day that Grayson lost the primary, McConnell told Paul that he would do — or not do — anything the Republican nominee needed to secure his win.

“At the end of the day, Mitch is a professional. His life is the Senate. His life is politics. It’s not cynical. It’s just how a leader works,” Grayson added. “He’s got to take care of his caucus.”

From the time Paul took office in January, the freshman has had regular weekly sit-down meetings with McConnell. The two talk consistently on the floor and in party luncheons. And on a staff level, McConnell’s personal office has been constantly involved with Paul’s shop, helping staffers to establish their office on the Hill and working together on Kentucky politics.

Most strikingly, Paul has gotten votes on several amendments, even on bills where more senior Senators have failed to persuade leaders to take up their case for a vote. In personal conversations and meetings with Senate Majority Leader Harry Reid (D-Nev.), McConnell has prioritized the inclusion of Paul’s offerings, a leadership source said.

On the vote to reauthorize the USA PATRIOT Act in May, Senate Judiciary Chairman Patrick Leahy (D-Vt.) did not get a vote on a bipartisan amendment drafted by his panel. But Paul got two amendment votes, including one on a controversial measure restricting national security officials from examining gun records.

Later that month, a budget Paul drafted, which would have eliminated many federal agencies, also received a vote, alongside one budget approved by House Republicans and another proposed by President Barack Obama. Only seven Republicans voted in favor of the Paul budget, including — at the last minute — McConnell.

“Well, I believe my Kentucky colleague is extremely serious about reducing government spending,” McConnell said about his vote then. “He has made that his issue. … He has my respect for continuing to press us to do more. He did a lot of work on the budget. And I think it deserved my support.”

Political strategists in Washington and Kentucky who have watched the growing McConnell-Paul relationship noted how “mutually beneficial” it has become. Indeed, it’s come a long way from when Paul won the GOP nomination in the state where McConnell is dean and the two had never spoken.