In the article, Trump criticized May's handling of Brexit, saying that she would likely "kill" any trade deals between the USA and the United Kingdom because she didn't take his advice.
His comments came during a joint press conference with British Prime Minister Theresa May.
"The president called out one of my colleagues, Kristen Welker of NBC News, as dishonest, he said NBC News was dishonest", he said. Gold stars all around for that sterling reporting job.
Acosta shot back, "Well we're a real network too sir". "Of course, it happens to be NBC, which is possibly worse than CNN", Trump groused.
Roberts, a chief White House correspondent, also stood by Welker, who was attacked by the president when she asked him if he was giving Russian President Vladimir Putin the "upper hand".
On Friday, he deployed the term against a surprise target - a British newspaper owned by his ally Rupert Murdoch - along with two US-based networks, CNN and NBC. She's as honest as the day is long. "To call her dishonest is unfair". I used to work at CNN, they have fine journalists there who risk their lives to cover the news around the world. Acosta said, referencing an earlier barb from the president.
Roberts had issued a statement defending Welker and his decision to ask a question after being called on by Trump in response to backlash for not supporting Acosta.
On social media, some journalists criticized Roberts - a former CNN employee - for not standing up for the network.
"No, no", Trump responded, calling the network "fake news".
Trump and Acosta have maintained a tense relationship since Trump took office, with Acosta often taking jabs from the president and his supporters.