I was up by that much

I was leading the game by this much !!

There're times when you're taking the lead or trying to take over in a sport game or a PC game. Imagine, that S.Korea 2:1 U.S.A up until the last 5 minutes in the second half. At 42 min, The United States team made an equalizer and right 2 min after that, they finally took the lead, and the moment the referee was going to end the game, they scored again and won the game. If the S.Korea player Sungwoo Lee played the game, he would probably make the face and say

" Damn we were up by that much !! "

Yes, you can use the expression here

We were up by that much !!

Literally, something was above ( up ) by the certain amount of something ( by that much ). Because the score or point was higher, the up preposition totally makes sense physically and conceptually. This is highly related to some point or score in a game, this is probably supposed to be used in a sport game event. Another example that ESL could easily think of is like below

We led the game until the last 5 minutes !!

It's more intuitive to use lead. You probably haven't heard of up by that much as an ESL learner. Take this expression and use it to make your English sound cooler.