On 13 August 2021, Vieira recorded the fastest pitch in NPB history at , a record previously held by Shohei Ohtani and Robert Corniel. On 1 September 2021, he set a NPB record for most consecutive mound appearances without giving up a run (32) by a non-Japanese player, breaking a record previously set in 2011 by Brian Falkenborg of the Fukuoka SoftBank Hawks. In 2021, he recorded seven saves and had a 2.76 ERA in innings with 38 strikeouts and was selected to the Nippon League All Star Game. On 23 December 2021, Vieira re-signed with the Giants for the 2022 season.
