The 37-year-old Bridgend cueman has earned career prize-money of more than £1million but had lost all four of his previous major finals.
He rid himself of the nearly-man reputation by fending off former world number two Maguire in impressive style at the tournament in Latvia on Sunday, with breaks of 59, 58 and 77 seeing him clinch a 5-2 victory. As well as the trophy, Day collected a £50,000 cheque.
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Day - who will climb from 18th to 15th in the world rankings - earlier fought off compatriot and former world champion Mark Williams in the semi-finals of the season-opening tournament, winning 5-4, while Maguire beat another one-time Crucible master Ken Doherty by the same margin in their last-four clash.
Irish veteran Doherty, 47, had the consolation of having reached the semi-finals of a ranking tournament for the first time since the 2011 Australian Goldfields Open.
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