Swift and Kelce were spotted at dinner in Buenos Aires and kissing after one of her performances.
The Chiefs' tight end, 34, was caught by Daily Mail at an airport in Argentina, boarding a private flight back to the U.S. in order to make it to football practice on Monday. The Kansas City team had a bye-week on Sunday which allowed Kelce to be with the "Bad Blood" singer, 33, for her concert over the weekend.
According to the outlet, Kelce left the Four Seasons early Sunday after a late night filled with dancing and singing alongside Swift's father Scott Swift and kissing his rumored girlfriend.
In the photos, Kelce could be seen wearing beige sweatpants and a sweatshirt and holding a bag of McDonald's as he boarded a private plane.
It was a quick turnaround for the football player who flew into Argentina on Thursday in time for Swift's first international Eras Tour concert -- which ended up being postponed to Sunday evening due to inclement weather.
Swift and Kelce were later spotted holding hands at dinner at a restaurant inside the Four Seasons.
Kelce first hinted at his international plans during the latest episode of his New Heights podcast, when he and his older brother, Jason Kelce, were recording an ad for a ticketing company and the Philadelphia Eagles player asked his younger brother if he had any shows he was looking forward to attending.
"I might just say f**k it and go somewhere nice. My skin's getting real pale, so I've got to go someplace sunny," Kelce responded. "Some place south, closer to the equator."
On Saturday, Swift surprised her beau with a lyric change to her song "Karma," making a direct reference to him to the shock and excitement of fans.
The "Midnights" singer was in the middle of her performance at Estadio Monumental when she belted out, "Karma is the guy on the Chiefs, coming straight home to me."
Immediately after Swift sang that line, the entire crowd went wild. Kelce was intently listening before she sang that line, and when she switched the lyrics the Kansas City Chiefs star was beside himself. So much so he covered his face in disbelief and excitement. And when Swift sang that lyric her dad, Scott (wearing a Kansas City Chiefs lanyard), tapped Kelce's shoulder as if saying "Did you hear that?!?"
There's video circulating on social media capturing the moment, and the comments section on a Taylor Swift fan account is littered with fans fawning over the moment.
One fan tweeted, "This is the best romcom I've ever seen in my life." Another fan added, "Scott's laugh ... he's so happy for this girl that she's so happy that she just changed the words."
Following the show, Swift and Kelce also gave fans a cheeky moment of PDA when she was seen running off the stage and jumping into his arms and kissing him in video posted online.
Fans who got to see the kiss can be heard screaming and cheering in the background as Kelce twirls his "lover" around and walks out of view.
Kelce and Swift were last seen together when she attended his Oct. 22 game against the Los Angeles Chargers. After the Chiefs secured the win, they left the stadium hand-in-hand and she gave him a kiss on the cheek, before heading out for a dinner date.
As for how the relationship is progressing, a source told ET that Kelce "is on the path to finding that special person in Taylor."