Is expiation obligatory for one who swore by "wa Rabbi" (by my Lord) that he would win the game to intimidate his opponents, and did not fulfill his oath?

If someone swears an oath regarding a future event, believing it will occur, but it turns out otherwise, then an expiation for breaking an oath is required of them. Jesting does not prevent an oath from becoming binding if the person intended to utter the explicit formula, based on the Prophet's (peace be upon him) saying: "There are three things which, whether done seriously or in jest, are binding: marriage, divorce, and revocation [of divorce]." The explicit formula of an oath is analogous to these; however, an implicit oath does not become binding through jest due to the absence of intention.