Allen lifted the title in 2018 but has not won a single match since and managed a high break of just 45 against fellow left-hander Hawkins, who was runner-up to Neil Robertson 12 months ago.
Hawkins, who will face either Judd Trump or Ryan Day in the quarter-finals, told the BBC: "I think the result flatters me a little bit. I think my safety won me the match really. I played a lot of good safety and created chances that way.
"I think if I was ultra-critical, I could have scored a little better but I kept Mark under pressure and I didn't do that much wrong - very few easy unforced errors - and I think that's made the difference in the end."
Hawkins recovered from a 55-0 deficit in the opening frame to win it on the colours, with breaks of 76 and 114 then extending his advantage.
Allen looked set to get on the scoreboard in a scrappy fourth frame only to overcut the brown and leave it over the corner pocket, Hawkins clearing up to move further ahead before making it 5-0 with breaks of 45 and 41.
Having recovered from 6-1 down to beat Ding Junhui 10-7 in the final of the UK Championship in November, there was still a glimmer of hope for Allen, but the Northern Irishman was unable to reproduce such heroics and Hawkins sealed a commanding victory.
"For once I didn't have that much time off (over Christmas), I had a couple of days off here and there but kept going up the club because I knew this tournament was coming up and this is not a place you want to come here and be underprepared," Hawkins added.
"I thought I'd keep my head down and today it's paid off."
A disappointed Allen was quick to pay tribute to Hawkins, telling Eurosport: "I probably should have won the first frame and had a couple of chances in frame four, other than that, I thought he was phenomenal.
"Some of his safety play was ridiculously good. There were a number of times I came to the table consecutively scratching my head, I had no shot at all.
"I said to him at the end, it's probably one of the best safety performances I've ever played against as a pro. Granted I missed a few balls as well, but you just have to credit Barry, he just froze me out. It was a phenomenal performance."