[{"gameId":"1a2b3c4d5e","rounds":[{"matches":[{"match_id":"1111abc1111","team1":{"team_id":"team8","score":0},"team2":{"team_id":"team2","score":0}},{"match_id":"2222abc2222","team1":{"team_id":"team6","score":0},"team2":{"team_id":"team5","score":0}},]}]}]

db.collection.aggregate([{"$match":{"gameId":"1a2b3c4d5e","rounds.matches":{$elemMatch:{match_id:"2222abc2222"}}}},{"$unwind":"$rounds"},{$project:{match:{$filter:{input:"$rounds.matches",as:"match",cond:{$eq:["$$match.match_id","2222abc2222"]}}},_id:0},}])