Meaning of 回戦 in Japanese

Definition of 回戦

かいせん(kaisen) 【回戦】

いっかいせん(ikkaisen) 【一回戦】

(n) first game; first round (of tennis, etc.)
ヒンギスが一回戦敗退の大番狂わせ。
It was a big upset when Hingis was eliminated in the first round.

きゅうかいせん(kyuukaisen) 【九回戦】

ヒンギスが一回戦いっかいせん敗退はいたいの大番狂わせおおばんくるわせ。

It was a big upset when Hingis was eliminated in the first round.