We lost several customers because we were short staffed and couldn't do the necessary sales work.
We lost an easy game that we were winning all the way until the end.
この場合の「取りこぼす」は使い方によって異なります。
ーWe lost several customers because we were short staffed and couldn't do the necessary sales work.
「私たちは人手不足で必要な営業が行えず、顧客を取りこぼした」
この場合は to lose customers を使って「顧客を取りこぼす」と言えます。
ーWe lost an easy game that we were winning all the way until the end.
「私たちは最後まで勝っていたのに、楽勝の試合に負けた」＝「勝利を取りこぼした」
この場合は、to lose an easy game を使って表現できます。
ご参考まで！
カナダ 
