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Taylor Swift On a Vegas Roll with Marcus Mumford!!!

Taylor Swift continues to blow fans away with one of the most well-received concert tours in years ... and this time a Mumford gave her an assist!

Taylor took her Eras Tour to Vegas Saturday night and the Allegiant Stadium was packed to the gills.

During her long set, she brought up a surprise guest -- Marcus Mumford.  The 2 performed "Cowboy Like Me,' with Taylor taking the lead and Marcus doing backup.

The fans were rabid, waiting more than 3 hours in line to buy some Swift merch. As for ticket prices ... well, an obstructed view seat on the secondary market went for north of $2k. Some of the premium tickets were topping $20k!!!

TikTok / @jjwatt

The concert, in which Taylor performs for hours without a break, has drawn high praise from the likes of former NFL star J.J. Watt, who was blown away at her kickoff concert in Glendale (aka Swift City) concert in Arizona.

Taylor is singing upwards of 40 songs in concerts that last more than 3 hours, which is insane, but the fans are lovin' it.

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