Lisowski had the chance to win his maiden professional title but missed the yellow and Maguire went on to triumph after winning a safety battle.
"Just lost 4-3 in final of PTC1," Lisowski tweeted after the match. "Had a chance to win but got too excited!"
Maguire, 31, lost in the finals of the German Masters and China Open last season.
“I came into this event with a different attitude,” he said.
“I was willing to battle and play a safety game if I needed to. This season I’m going to try not to push the boat out too much. If it doesn’t work then next year I’ll go back to going for everything.
“I always start the season the same way, knowing that if I can get my name on a trophy I’ll have done well. I don’t count this in the same way as a ranking event but it gives me confidence and there are plenty of big tournaments to try to win.
“I think everyone has realised now that the ranking points from the PTC events are important. Plus £10,000 is a lot of money to be won in a weekend. It’s easy to be up for it on the final day.”
Maguire hit breaks of 84 and 75 to take a 2-1 lead while Lisowski fashioned a break of 70 in the second.
The 21-year-old Lisowski came from 33-0 to win the sixth frame and force the decider and could have cleared the table from 42-0 in the final frame but missed the yellow when he was on 56.
Lisowski beat flat-mate Judd Trump 4-3 in the quarter-finals and two-times world champion Mark Williams 4-3 in the semis, while Maguire beat Barry Hawkins 4-3 in the last eight and Andrew Higginson 4-1 to book his place in the final.