"I want to congratulate Mark on a brilliant tournament. He is a very consistent player, so I'm pleased to have won," said the winner, who earns £200,000 for the triumph.
"Playing Mark, you expect he will take you all the way and sometimes the worst thing you can do is build a lead because you never feel you are near the winning line."
O'Sullivan, who is only ranked 24 in the world after missing several tournaments, was playing in a record 10th Masters final but his first since Selby had triumphed 10-9 five years ago.
It was the fifth time in seven years Selby - labelled 'the Torturer' by O'Sullivan because of his steely determination - had reached the final, but he could only look on as his in-form opponent took control.
The defending champion looked nervy and missed chances to win the seventh frame to close to 5-2, eventually losing on a re-spotted black.
O'Sullivan - champion in 1995, 2005, 2007 and 2009 - capitalised, before going on to take the final frame of the session.
O'Sullivan plays 'snooker from the Gods'
He continued where he left off, taking the evening opener to make it 8-1 in the best-of-19 frame final.
Selby, nicknamed the 'Jester from Leicester', finally had something to smile about when he pulled one back after the world champion missed a black in the ninth frame.
But the 30-year-old, who also won the tournament in 2008 and 2010, would claim just two further frames.
"Ronnie started great," said Selby, who collected £90,000 as runner-up. "I had a few shots but he is fantastic at taking his chances.
"I had a good chance in the fourth frame of the evening session but, when he is in front, he steamrollers you.
"The damage was done in the first session and you need to be on top."
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