In the third ballot of the Tory leadership contest on Monday evening, Mr Sunak got 115 votes, Ms Mordaunt 82, Liz Truss 71, Kemi Badenoch 58 and Tom Tugendhat 31.
Attorney General and right-winger Suella Braverman, who was knocked out of the contest last week, had thrown her weight behind Ms Truss.
That endorsement, however, appears to have not been enough to push the Foreign Secretary into second place.
The ballot came after another fraught day of campaigning in the Tory Party leadership contest, despite concerns being expressed publicly about the growing divisions within the party over the contest.
Most notable on Monday was the accusation that Ms Mordaunt missed ministerial meetings because she was plotting her Tory leadership bid.
The trade minister’s absence from meetings forced colleagues to pick up the pieces, Britain’s international trade secretary Anne-Marie Trevelyan earlier alleged.
In a sign of the concern about the way the leadership race is being conducted, Mr Sunak and Ms Truss confirmed they did not want to take part in a Sky News debate planned for Tuesday – prompting the broadcaster to cancel the show.
“Conservative MPs are said to be concerned about the damage the debates are doing to the image of the Conservative Party, exposing disagreements and splits within the party,” a Sky statement said.
UK Labour leader Sir Keir Starmer said he is “astonished” by candidates withdrawing from the debate, arguing that it demonstrates a lack of “confidence”.
He told reporters at a central London bank: “I can see, based on what I’ve seen in the debates so far, why they want to do so because this is a party that is out of ideas, out of purpose, they’re tearing each other apart.”
The leadership contenders – Mr Sunak, Ms Truss, Ms Mordaunt and Ms Badenoch – have already taken part in debates on Channel 4 and ITV which have seen the would-be prime ministers taking primetime pot shots at each other.
International Trade Secretary Anne-Marie Trevelyan says there have been ‘a number of times’ where Penny Mordaunt ‘hasn’t been available and other ministers have had to pick up the pieces’ in recent months.#CallTheCabinet | @annietrev | @NickFerrariLBC pic.twitter.com/aYdkoO1JGj
— LBC (@LBC) July 18, 2022
The exit of Mr Tugendhat from the contest was not unexpected, with the Tonbridge and Malling MP trailing behind rivals in the bid for Tory MP backers.
He had addressed his likely fate head-on earlier, dismissing any suggestion that he would drop out.
The PA News agency understands that at the behind-closed-doors hustings organised by the backbench 1922 Committee, he told MPs that it had been suggested to him that he should step aside and back another candidate.
He said: “It will come as no surprise that some have suggested I could leave with a job as well. But my view is clear. It is not for me to make that decision – it is for you.”
Tweeting after the contest, he said: “Although it wasn’t to be today, I am immensely proud of the positive vision we put forward for our country.
“Thank you to all those who supported me and believed in #ACleanStart.
“This is only the beginning!”
— Penny Mordaunt (@PennyMordaunt) July 18, 2022
Ms Mordaunt’s record in office came in for further attack from Ms Trevelyan on LBC Radio on Monday morning.
Asked about Ms Mordaunt’s grasp of details, Ms Trevelyan said: “We all do our jobs in different ways.
“Understandably, perhaps, now it’s clear, Penny has for the last few months spent some of her time focused on preparing her leadership campaign, for which I have utmost respect, that’s how this system works.”
Ms Trevelyan added: “There have been a number of times when she hasn’t been available, which would have been useful, and other ministers have picked up the pieces.”
But former minister Harriet Baldwin, an ally of Ms Mordaunt, said: “Having worked with Penny Mordaunt for a number of years, I can confirm this is not true.
“She is one of the most hard-working ministers and constituency MPs I know. I look forward to Penny continuing to put forward her positive vision for Britain.”
Cabinet minister Kit Malthouse said he expects the Tories to pull together in a “spirit of harmony and love” after the leadership battle.
“All political parties are standing coalitions and the Conservative Party is the same,” he told Sky News.
“A vigorous exchange of ideas, in what is a challenging time for the country, should be expected when you are talking about such important issues and the leadership of a G7 nation.
“If it was just a polite agreement and consensus across the board, there wouldn’t be much point in having a competition at all.”
Mr Malthouse has not publicly declared his support for any of the candidates to succeed Mr Johnson.
A series of votes among Tory MPs this week will narrow the field down to a final two, who will then face a summer of campaigning for the support of party members in a final vote.
The new leader will be announced on September 5th and is expected to become prime minister the following day.
Mr Sunak said that if he is successful his first foreign trip will be to Kyiv to stress the UK’s continued support for Ukraine in its fight against the Russian invasion.
He told The Sun: “I will reinforce our policy of total support for Ukraine that Boris has so ably led.”
But Ms Mordaunt said her campaign has the support of 10 Ukrainian MPs.
Meanwhile, Ms Truss seized on analysis by the Centre for Economics and Business Research which suggested that tax revenues in 2024/25 will be around £60 billion more than the Office for Budget Responsibility estimates, partly due to the impact of high inflation.
A spokeswoman for Ms Truss said: “The CEBR analysis shows that there is money for tax cuts whilst still bringing debt down.”