On 25 July 2012, Osmar signed a two-and-a-half-year contract with Thai club Buriram United F.C. for an undisclosed fee.[4] He made his debut on 1 August, appearing in a Thai FA Cup match against Chonburi F.C. and going on to win both that tournament and the Toyota League Cup in his first year.
On 26 February 2013, Osmar made his debut in the AFC Champions League, in a match against Vegalta Sendai, acting as team captain and scoring a goal in the 1–1 away draw. On 1 May, Buriram became the first team from the nation in a decade to reach the knockout rounds of the AFC Champions League,[5] and he topped his side's scorers list at three.[6]
FC Seoul
On 31 December 2013, Osmar moved teams and countries again, joining FC Seoul on a three-year deal and becoming the first Spanish footballer to ever play in South Korea.[7] Ahead of the 2015 season he was appointed vice-captain,[8] appearing in the all matches and minutes to set a new record for a foreign field player in the K League 1.[9]
Before the start of the following campaign, Osmar was chosen as Seoul's new captain, becoming the first foreigner in the club's history to hold the position.[10][11] Throughout the season, he helped the team win the national title,[12][13] becoming the first Spanish player to ever do so in the process.[12]
On 21 February 2018, he joined J1 League's Cerezo Osaka on loan.[14] On 18 December of the same year, Osmar signed a new three-year contract with Seoul.[15]
At the end of the 2023 season, Osmar left Seoul after the club had decided against renewing his contract.[13][16] Throughout his spell, he made a total amount of 344 appearances for the South Korean club, scoring 25 goals and 12 assists in the process;[13][16] at the time of his departure, he held the club record for the highest number of appearances by a foreign player,[13][16] and was second only to Go Yo-han for all-team appearances.[13]
^オスマル選手 期限付き移籍加入のお知らせ [Announcement of footballer Osmar's deadline transfer] (Press release) (in Japanese). Cerezo Osaka. 21 February 2018. Retrieved 22 February 2018.
^"FC서울 오스마르, 임대복귀 및 3년 재계약" [FC Seoul's Osmar, return to organization and three-year renewal] (in Korean). FC Seoul. 18 December 2018. Archived from the original on 11 October 2016. Retrieved 19 December 2018.