I was dropping with fatigue and could not keep my eyes open.

我快要累倒了，眼睛也睁不开了。

《牛津词典》

I can hardly keep my eyes open, and the dog Toto is asleep already.

我几乎睁不开眼睛了，而小狗托托已经睡着了。

youdao

Richard: I can hardly keep my eyes open. If only we could bottle the fresh air.

我很难坚持睁开我的眼睛。只要我们能把新鲜空气装在瓶子里。

youdao

The shop provided tea in a samovar, which tasted a little fishy, but I drank one mug after another to soothe my throat and keep my eyes open.

NEWYORKER: The House Behind a Weeping Cherry

My heart went out to you when I saw you trying to keep your eyes open during an MLK Day sermon.

WSJ: Excerpt: From the Letters of George H.W. Bush