The pair, who were the final two in last year's show, entertained crowds as they sang together on Friday night.
Saara and Matt teamed up to perform Subeme La Radio / Turn Up the Radio, Enrique Iglesias' new track which Matt featured on for the UK release.
"It got a bit wild on stage yesterday ✨Always loving @MattTerry93 😘❤️#nofearsummertour #nofear2017" Saarah tweeted after the performance.
Matt teamed up with Enrique as well as rapper Sean Paul on the new version of Enrique's Latin pop hit.
— Matt Terry Brasil (@MattTerryBrasil) August 26, 2017
The song was released to download last month and Matt - who grew up in Spain - was over the moon with the collaboration.
"Enrique asked me to be part of this track, which is amazing," he said. “We’re label mates and both signed to RCA but mainly it’s because I have a Spanish background.
“I sing the second verse and the second chorus. We did it out in Miami. They said, ‘Enrique wants you’."
Matt added: “I used to sing his songs as a kid in my room in English and Spanish. I’ve been working out a lot. I’m prepping myself for a sexy Spanish music video.
“Forget Simon Cowell’s unbuttoned shirts — I’m taking all the buttons off!”
Matt beat Saara in the final of last year's X Factor competition but both have gone on to sign big money record deals.
Matt has penned a contract with RCA Records while Saara signed a joint deal with Sony Music in the UK and her home country of Finland.
Both are expected to release albums by the end of the year alongside third placed 5 After Midnight.
The boy band trio also signed a record deal, joining Simon Cowell's own Syco music label.
Meanwhile The X Factor will return very soon for a brand new series.
ITV confirmed last week that the 2017 run will begin on September 2, next weekend.