"It's always nice when teams around you are interested because it means you're doing something right.
"I was always focused on coming back here and getting fit. At the end of the day I was contracted to Albion anyway and I was concentrating on kicking off the season here.
"It's an ambitious club and I'm looking forward to kicking off the new season in the Premier League."
After playing a key role in West Brom's second-placed finish in the Championship last season, Dorrans won the club's player of the year award and the Professional Footballers' Association fans' player of the year.
And his fine form also earned the former Livingston man, who joined West Brom in July 2008 for £150,000, three Scotland caps.
"I'm delighted Graham has signed a new long-term contract, which is fully deserved," said Di Matteo.
"There has been a lot of media speculation about Graham's future but it hasn't affected him one bit.
"Ever since he has reported back for pre-season training, his attitude has been as spot on as it always is and I know for a fact how much he's looking forward to the new season.
"The exciting thing is that Graham knows he still has a lot of work to do and is yet to reach his full potential."
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