Simpson added a new champion's belt to his collection at the weekend when he captured the vacant WBC international Silver super-featherweight title at the Emirates Arena on Saturday night.
The main support to world champion Ricky Burns at the Glasgow venue, the 29-year-old former British and Commonwealth featherweight champion produced a career-defining performance that epitomised his fighting spirit.
Simpson fought with the heart of a lion to unseat Mongolian warrior Choi Tseveenpurev by margins of 117-112, 116-112 and 116-113 on the judges' scorecards to register his 25th win in 34 contests.
Now Simpson has the dual target of a summer showdown for Welshman Gary Buckland's British crown quickly followed by a world title bout, almost certainly on the Burns bill when the Coatbridge boxer makes his next defence in September.
Simpson had to dig deep to overcome 41-year-old ring veteran Choi, a former two-time world champion who was looking for his 37th win in his 43rd bout. Despite a 12-year age difference, Choi showed no signs in the early stages of having slowed up, making Simpson miss in the opening round and then tempting his opponent into a brawl in the second.
Choi, with the face of a warrior and the mindset of one, hurt Simpson with a right to the left side of his body 30 seconds from the end of the round and it was a warning of the older man's enduring power.
Simpson edged the next round when he resumed a more measured approach and out-boxed his opponent with an effective jab, also staying just out of range of Choi's big punches.
But Choi emerged on top in the fourth round when he once again drew the Scot into a tear-up and after both had got off four punches each in a rapid fire exchange, Choi bloodied Simpson's nose.
But Simpson gradually took control of the centre of the ring and, in spite of shipping several body shots, he wore Choi down in the second half of the fight.
Simpson reflected: "Choi was a really tough opponent, as I knew he would be going by his record, but I wasn't expecting quite as hard a fight.
"I was given only six weeks' notice to prepare myself and felt sick after the fight and again on Sunday morning and didn't sleep too well.
"Nobody wanted to fight Choi because of his record although I actually offered to box him a year or so ago. But the money wasn't right at the time.
"The fact the title was vacant meant I could have fought anyone.
"But I never have it easy and I just got on with the job at hand.
"I'm glad I did and that it's paid off. I'm the mandatory challenger for Buckland's British title and that fight's going to happen sometime in July after Ricky Hatton won the purse bid.
"That's the fight I am setting my sights on. Hopefully, the world title shot will materialise but I am not holding my breath."
The forthcoming bout with Buckland will be Simpson's 10th British title contest, the best of which was his stunning points win over Martin Lindsay in December 2010.
Simpson, never the luckiest of boxers and the victim of several highly questionable decisions, has also held the WBU featherweight title and the Celtic super-featherweight belt in an 11-year career.
Meanwhile, Burns retained his WBO lightweight title after the Coatbridge boxer's mandatory challenger, Jose Gonzalez retired on his stool immediately prior to the 10th round.
The Puerto Rican was ahead by three rounds on all three judges' scorecards when he dramatically quit with a suspected fractured wrist.