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Keith Urban looks like he's ready to move on from Nicole Kidman ... not just in his marriage, but in his music too.

A clip making rounds on social media shows Urban performing "The Fighter" during a recent performance -- a song he wrote about Kidman.

However, Keith switches up the lyrics ... changing the line, "When they're tryna get to you, baby I'll be the fighter" to "When they’re tryna get to you, Maggie, I’ll be your guitar player." Getty

For context ... Maggie Baugh is one of Urban's utility players and was onstage with him when he made the switch.

She posted the clip on Instagram on Saturday, Sept. 27, with the caption, "Did he just say that 👀." Gallery Launch Gallery Getty

TMZ broke the story ... Nicole filed for divorce Tuesday, after the coupl

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