A smile lifted the corner of his mouth.

他的嘴角挂着微笑。

《牛津词典》

She flicked a crumb off the corner of her mouth.

她轻轻擦去了嘴角的面包屑。

《柯林斯英汉双解大词典》

The corner of her mouth, where one looks first, is almost withered up.

她的嘴角，第一眼看到的地方，几乎枯萎了。

youdao

Take the full-grown moustache, for example, with down-turned ends at the corner of the mouth.

BBC: Moustaches under threat

There was a twist in one corner of her mouth, as if something were not right in her stomach.

NEWYORKER: Ziggurat

He had this black cold sore at the corner of his mouth, and his eyes had sunk into his face like little pits.

NEWYORKER: The Pura Principle