Saki is best described as light yuri. There are a lot of romantic two girl friendships, but no consumated relationships.
In Japan, the term "shoujo ai" is partially associated with lolicon. Saki has some high school age loli characters, but they are part of a much larger cast that includes some adult characters. With one exception, the under high school age characters aren't sexualized.
Most of the high school mahjong teams include girls who have crushes on other girls. Several of the crushes are reciprocated, leading to romantic two girl friendships. There is also one character that is lesbian or at least bisexual.
The title character has progressed as far as hand holding with intertwined fingers. She and the main supporting character share dozens of romantic moments together.
One of the most attractive side characters hugs her teammate while saying that she loves her. While that spur of the moment confession is not reciprocated, it's not unwelcome.
Those are the most intimate yuri relationships, but there are several other lighter yuri relationships.
Achiga-hen episode of side-A
One of the high school teams includes a romantic two girl friendship. One of girls often uses the other girl's lap as a pillow. They also hold hands with fingers intertwined.
There is some correlation between the girls with yuri relationships and those with mahjong related supernatural powers. However, this can simply be a coincidence arising from the fact that there are many yuri characters and many characters with supernatural powers.