During a debate that frequently fizzed with tension, Mr Masters struggled to say if he had taken down that material, and also removed a more hardline position on abortion rights - a position his Democratic opponent Mark Kelly said was part of his “dangerous” views.
In August, a page on his website called “The Masters Plan” read: “We need to get serious about election integrity. The 2020 election was a rotten mess – if we had had a free and fair election, President Trump would be sitting in the Oval Office today and America would be so much better off.”
After winning the Republican primary for the Senate race in Arizona, outfits such as CNN reported how the 36-year-old had changed his website, apparently as part an effort to moderate his image for the general election. Now, that page simply reads: “We need to get serious about election integrity.”
The debate on Thursday comes a month before voters across the country go the polls in the mid-term elections, and while polls give Mr Kelly a lead of around four points, the seat is high on the target list of Republicans who want to regain control of the Senate.
On Thursday night at the event in Phoenix, Mr Masters, 36, whose campaign is being bankrolled by tech billionaire Peter Thiel, was asked if he thought Joe Biden was the elected president.
“Joe Biden is absolutely the president. I mean, my gosh, have you seen the gas prices lately,” he replied.
The moderator asked if he thought Mr Biden was legitimately elected.
“I’m not trying to trick you. He’s duly sworn certified. He’s the legitimate president. He’s in the White House and unfortunately for all of us, Joe Biden’s the president. He has been for the last two years,” he said.
“And everything he’s touched in the last two years has turned well, to you know what. Everything’s on fire. It’s Joe Biden’s fault. I wish he weren’t the president. He is.”
Mr Masters then talked about how Mr Biden had become president.
“I think it’s a problem that the FBI forced Facebook, they pressured Facebook and other big tech companies, to censor true information about Hunter Biden’s crimes in the weeks before the 2020 election. And so millions of Americans didn’t get to read about that didn’t get to read about Hunter Biden.”
He was asked if he thought the election was “rigged”.
“I suspect that if the FBI didn’t work with big tech and big media to censor the Hunter Biden info or the Hunter Biden crime story,” he said.
“Yeah, I suspect that changed a lot of people’s votes. I suspect President Trump would be in the White House today, if big tech and big media and the FBI didn’t work together to put the thumb on the scale to get Joe Biden in there.”
Mr Kelly, 58, a former astronaut who was elected in 2020 in a special election, is fighting for reelection, said the only reason people were talking about the issue was because “my opponent Blake Masters, put out a video questioning who won the president presidential election here in the state of Arizona”.
Mr Masters, a hedge fund investor, also changed his website to remove more extreme positions about abortion. Previously he had stated he supported a “federal personhood law” and stated: “I am 100% pro-life.”
On Thursday, Mr Masters said he supported a 15-week abortion ban, which came into effect in September after the Supreme Court overturned Roe v Wade.
He was asked if he changed his website.
“I encourage people to go read my website now. It is still the most pro-life, most detailed agenda of any Senate candidate running nationwide. I’m pro-life. I’m proud to be pro-life. I will never run from that,” he said, dodging the question.
Libertarian candidate Marc Victor, who was also debating, then spoke.
“This evasiveness from Blake Masters is exactly why you should have a principle and stick with it,” he said. “You asked him specifically did he scrub his website? And he said you could go to my website now and look at it. That’s evasion.”