Sens. Joe Manchin (D-W.Va.) and Lisa Murkowski (R-Alaska) broke party ranks Friday morning on a key vote for Supreme Court nominee Brett Kavanaugh, with Manchin voting to advance the nomination to a final up-or-down vote and Murkowski voting to block it.

The Senate voted 51-49 to end debate on his nomination, setting the stage for a confirmation vote as early as Saturday afternoon.

Manchin, who is facing reelection this year in a state President Trump won by double digits in 2016, had said the FBI's supplemental report would factor heavily into his decision on whether to support Kavanaugh, and the document was made available to senators on Thursday for private viewing.

Manchin is key because if he votes for Kavanaugh Saturday, Republicans can confirm the judge even if Sen. Susan Collins (Maine), an undecided Republican, votes no.

Collins, who voted with GOP leaders to advance Kavanaugh but has yet to announce her position on a final confirmation vote, will unveil her decision in a floor speech scheduled for 3 pm Friday.

Murkowski joined with two other Republicans last week in pressuring Senate Majority Leader Mitch McConnell (R-Ky.) to delay the floor vote on Kavanaugh to give the FBI more time to investigate allegations of sexual assault against Kavanaugh.

Murkowski is not up for reelection until 2022 and viewed as less concerned about a primary challenge.

She later told reporters that she did not make her decision until walking onto the Senate floor Friday morning.

"I have been wrestling to really try to know what is fair and what is right and the truth is that none of this has been fair. It hasn't been fair to the judge. But I also recognize that we need to have institutions that are viewed as fair but if people who are victims, people who feel that there is no fairness in our system of government, particularly within our courts, we've gone down to a path that is not good and right for this country," she said.

She announced her no vote so softly that colleagues had trouble hearing what she said, as did members of the press who were gathered in the galleries above the floor.

Senate Democratic Whip Dick Durbin (Ill.) said he was not surprised that Murkowski bucked GOP leaders.

"I've worked with her. She's stood up in the past on things. She's a pretty independent person. She was with me on the Dream Act, from Alaska!" Durbin said, referring to legislation to protect undocumented immigrants who arrived in the country as children from deportation.

Murkowski met with dozens of Alaskan women who shared their stories of sexual assault in her office Thursday.

Sen. Jeff Flake (R-Ariz.), the other previously undecided Republican who joined with Murkowski to delay the floor vote on Kavanaugh for a week, voted Friday to advance his nomination.

Flake told reporters after the vote that he will support Kavanaugh for confirmation on Saturday.

Every other senator who voted on the procedural question to advance Kavanaugh voted along party lines.

-Jordain Carney contributed