Derrick won his tennis match and qualified for the semifinals.

qualified 是动词 qualify 的过去式，qualify 由词根 qual（质量、资格）和后缀 -ify（使...）组成，意思是"使具备资格"或"取得资格"。 在这里 qualified 表示"获得资格/晋级"，指通过赢得比赛获得了参加半决赛的资格。