Luck out
Definition 1 of 2
Pro Tip 1/3Chance Success
Use 'luck out' when an unexpected good thing happens without planning. 
I lucked out when I found a $20 bill on the sidewalk.
Pro Tip 2/3Positive Outcome
'Luck out' implies a positive outcome which could have been bad. 
They lucked out with the weather during their beach wedding.
Pro Tip 3/3Not Skill-Based
It's used when success is due to luck, not skill or effort. 
He didn't study but lucked out by guessing the right answers.