Oprah Winfrey sprang a November surprise for Democrats in the midterm elections as the US TV host endorsed their candidate John Fetterman in Pennsylvania’s hotly contested Senate race, snubbing his Republican rival Mehmet Oz whom she originally made famous on her daytime talkshow.

Until now, Winfrey had said she would leave the election to Pennsylvanians, but on Thursday evening she changed that position in an online discussion on voting in next Tuesday’s election.

“I said it was up to the citizens of Pennsylvania … but I will tell you all this, if I lived in Pennsylvania, I would have already cast my vote for John Fetterman for many reasons,” Winfrey said, before going on to urge listeners to vote for Democrats running for governor and Senate in various states.

The Pennsylvania seat has for months been seen as the most likely pickup opportunity for Democrats in the evenly divided Senate.

Polls show a close race between Fetterman, the state’s lieutenant governor, and Oz, a celebrity heart surgeon who is endorsed by former president Donald Trump.

In a sign of how high the stakes are, Trump will return to Pennsylvania on Saturday to campaign for Oz, while Joe Biden and the former two-term Democratic president Barack Obama will campaign for Fetterman that same day.

Oz left Oprah’s show after five years and 55 episodes to start his own daytime TV program, The Dr Oz Show, which ran for 13 seasons before he moved from New Jersey to Pennsylvania to run for the Senate.

The Senate seat is being vacated by the retiring Republican Pat Toomey.

Fetterman’s race is among those that have grown tighter in recent weeks as polls showed rising support for Oz, who has made much of the fact that Fetterman had a stroke this spring during the campaign and spent much of the summer convalescing.

Fetterman has been declared fit for work by his medical experts but has needed some adjustments to accommodate auditory processing.

At a recent debate, in order to accommodate Fetterman’s condition, which he said was improving daily, two 70-inch monitors were placed above the heads of the moderators, which showed the transcribed text of their questions, and the text of Oz’s responses.

The candidates fiercely clashed over abortion rights, with Fetterman strongly pro-choice.

His endorsement by Winfrey – an icon to many Americans, particularly women and African Americans – is seen as a useful boost to Democrats’ chances in that race.

Fetterman celebrated with the kind of witty burn on social media he has become well-known for, especially over the summer when he was physically absent from the campaign trail but repeatedly taunted Oz’s New Jersey connections.