Three crucial Republican senators said Tuesday they will vote for a procedural motion in Republicans' push to repeal Obamacare, a boost to the GOP effort in what is expected to be a tight vote.

The support from Sens. Rand Paul, Dean Heller and Shelley Moore Capito makes passing the motion to proceed later Tuesday a much more realistic goal. All three opposed previous versions of a repeal or replacement plan.

Republicans can only lose two votes and still approve the procedural motion. Sen. Susan Collins, R-Maine, is a firm "no" on the motion, while some other Republicans remain undecided.

Paul tweet: If this is indeed the plan, I will vote to proceed and I will vote for any all measures that are clean repeal.

Paul, the conservative from Kentucky who has opposed some iterations of the Republican Obamacare replacement plan, has backed a 2015 bill that repeals parts of the landmark health-care law. Congress approved that plan knowing that then-President Barack Obama would veto it.

In tweets, Paul said he will support any and all measures "that are clean repeal." He highlighted a plan that repeals "mandates and taxes" without "new spending and bailouts."

Paul: If this is indeed the plan, I will vote to proceed and I will vote for any all measures that are clean repeal.

Heller, the senator from Nevada, vehemently opposed a previous Obamacare replacement plan. He said in a statement he would vote "to move forward and give us a chance to address the unworkable aspects of the law that have left many Nevadans — particularly those living in rural areas — with dwindling or no choices."

"If the final product isn't improved for the state of Nevada, then I will not vote for it; if it is improved, I will support it," Heller said.

Capito said in a statement that she will "continue to push for policies that result in affordable health care coverage for West Virginians, including those who are in the Medicaid population and those struggling with drug addiction."

Several GOP senators have expressed concerns about what a so-called clean repeal, as passed in 2015, would do to insurance markets.

The Senate could take a complicated path if the motion to proceed passes. One possible route could end with a so-called skinny repeal, according to NBC News, which cited two Senate sources.

The Senate would "move on to debate and vote on a variety of approaches to the bill," like the repeal now and replace later plan that Paul supports but is expected to get blocked, NBC reported.

The chamber could then field some version of the replacement plan that stalled out recently, which may also fail. After that may come a vote for a partial, "skinny" repeal that would eliminate the individual mandate penalty, the employer mandate penalty and the medical device tax, according to NBC.

A spokesman for Senate Majority Leader Mitch McConnell declined to comment to CNBC on what the Senate would do next if the motion passes.