At the 2021 US Open partnering Jackson Withrow they defeated top pair Nikola Mektić and Mate Pavić in the first round in 75 minutes.

At the Korea Open he partnered Raven Klaasen to win his second title in two weeks defeating Nicolás Barrientos and Miguel Ángel Reyes-Varela in straight sets.

At the 2023 Miami Open they reached the semifinals of a Masters for the first time but lost to eventual champions Santiago González and Édouard Roger-Vasselin.

At the last Masters of the season in Paris the pair reached the quarterfinals defeating sixth seeds Máximo González and Andrés Molteni.

[10] Lammons and Withrow won their sixth title as a pair at the 2024 Libéma Open defeating top seeds Wesley Koolhof and Nikola Mektić.

[14] At the 2024 US Open, Lammons reached the semifinals of a Grand Slam for the first time in his career, partnering Withrow, with wins over three-time defending champions Joe Salisbury and Rajeev Ram[15] and 13th seeds Wesley Koolhof and Nikola Mektić.

[17] At the 2024 Shanghai Masters, they reached the quarterfinals but lost to Wesley Koolhof and Nikola Mektić which halted their attempt to move one position up above their opponents in the ATP doubles race from their current place of No.