Khan delivered a punch-perfect performance to romp to a magnificent unanimous points decision at Manchester's MEN Arena.
It makes him the third youngest post-war British world champion at 22 years, seven months and 10 days.
A late venue change meant Khan returned to the scene of his shock 54-second loss to Breidis Prescott last year.
But victorious Khan insisted: "I've proved everyone wrong - who'd have thought I'd be a world champion inside three fights from that defeat?
"In the later rounds I got tired. But I never doubted myself.
"I knew it would be tough to come back and prove the critics wrong."
He coasted the first round despite a a couple of warnings for holding down from South African referee Stanley Christodoulou.
Kotelnik, 31, started throwing more leather - and with doubts about the Khan's chin it was edge-of-the-seat stuff whenever the champ came forward.

The young Briton was caught by a short right hook, but he stood his ground and covered up well.
Trainer Freddie Roach has rebuilt and remodelled Khan since they came together after that shattering Prescott loss.
The American ironed out Khan's fundamental mistakes, spending hours every day working on his defence.
It has worked - but Kotelnik was still landing punches and at the end of round four a couple of overhand rights caught the 2004 Olympic silver medallist high on the temple.
Kotelnik was trying to pierce Khan's high guard and to get inside the Brit, who was bouncing around the ring getting out of range to dodge the bullets.
Ringsiders stood and cheered when the challenger was caught by a right counter in round six.
And as the pair went into the final quarter of the fight, it became clear that Kotelnik - who was making his third defence - clearly needed a knockout to cling to his crown.

By the ninth, Khan knew he was mile ahead. Even when he was caught by a right hook and left cross, he got on his feet and moved.
The tactics had been perfect and the discipline even better.
Trainer Freddie Roach would like his boy to face Mexican superstar Erik Morales in America next - then return home to face Ricky Hatton.
And Roach said: "The guy threw a lot of a pressure on us. I thought he'd be more passive but Amir fought a good fight. I thought he won every round."
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This article has 18 comments
great win by khan was a big critic of his before and just after the prescot fight but wen he fought that fagen olsen new then we were watching a difrent fighter done the same ot barrera and again last night hes realy quik learner and could be a great champion for years to come shouldnt face hatton though at this stage hattons a seasoned pro aint beleivein all this hattons past it cos pac wiped him out same as with khan you get caught flush your goin down simple as hattons gota point to prove and would be a shame to lose the respect khans earned by losein to hatton which he would should fight some mandtorys keep learnin and in 5 more fights then face the big boys hatton stil a good fighter2 loses to p4p n1 aint nothin to be wrote off aboutkhan lost much worse to a much craper fighter in half the time not so long ago but hatton gets the stick he was p4p number 8 before the pac fight
By lee moor.. Posted July 19 2009 at 9:19 PM.
Khan does have a glass chin but Hatton is rubbish. Hatton doesnt seem to have much of a chin the way he kept falling down like a sack against the Pacman who destroyed him. He totally humiliated him.
By Qasim.. Posted July 19 2009 at 3:23 PM.
what a magnificent fight from amir khan last night he was diffrent class his footwork and hand speed were lightining fast there is no doubt freddie roach has improved amir khan in to a world class operator his defence and boxing brain is top draw amir allways had the ability but he would look for the knockout punch that was down to lack of experiance being as young as he is but to bounce back from a defeat and become world champion shows this boy has the heart of a lion great character and mental strength he has done britain and the country proud im delighted for the boy he is a smashing kid who has his feet on the ground welldone and congratulations
By james,leeds.. Posted July 19 2009 at 2:23 PM.
Good win, Kotelnik looked ordinary, and Khan did the business with his hand speed. However, similar to Calzaghe, he doesn't punch hard enough, and (crucially) unlike Calzaghe, he doesn't have a chin of iron.
If Amir comes up against someone who will trade blows and not allow him to fight one the outside (i.e. Hatton), he will get found out.
I suspect that this will prevent Amir from becoming a great fighter.
By Sedz83.. Posted July 19 2009 at 12:54 PM.
Im a big follower of boxing, Im suprised how well khan did! Dont worry about the critics mate britain is a lover of the underdog and you are no underdog! khan is still 22! khan is still learning and he is champ, unbeleiveble! Hatton only fights one way now (*he cocks back then throws leaving him terribly exposed) he hasnt the age to adapt no more the way khan has proven in three fights! Bring on hatton if thats what the public wants. Roach and team wildcard has seen something in Khan that some british poeple cant see, Khans on the verge of breaking america, watch the acclaim he gets there!
By Dean.. Posted July 19 2009 at 12:03 PM.
A long way to go yet! Lets not excited.
By Crazy Joe.. Posted July 19 2009 at 11:59 AM.
You idiots,
If Khan had a 'glass chin' then the shots Kotelnik hit him with (Which were harder than Gomez, Limmond, etc) would have had him down.
Truth is he was drained @ 135lb.
By Clint.. Posted July 19 2009 at 11:20 AM.
bring on the hatton did u all c wat pacmam did to him lol hatton was a lost kid in ta ring well done amir am proud of you my money well spend
By habib haji.. Posted July 19 2009 at 11:04 AM.
fair play to you Amir but i do feel hatton wouldnt give you the room you need in the ring.
By dai dap.. Posted July 19 2009 at 10:17 AM.
didnt watch the fight glad that khan won although if he fights someone like hatton it will end in tears jus coz khan is comin on now, especially after the shock bredis ko, gettin in the ring with someone of hattons pedigree will expose khan for the true fighter he is!! cocky with a glass chin!! hatton is a legend besides IF, and a v big IF, he were to beat hatton who does he fight after?? Mayweather, paquiao?!! anyone out there honestly think that khan would beat either of those????
By the wiz.. Posted July 19 2009 at 10:17 AM.
well dome lad, i swelled up with pride when i saw result
By chriso.. Posted July 19 2009 at 10:10 AM.
Congratulations mate. Job well done.
By Dominic Osei.. Posted July 19 2009 at 9:54 AM.
Congrats Amir Khan, well done!
By Mani .. Posted July 19 2009 at 10:10 AM.
well done amir you grew some balls at last
By csowden.. Posted July 19 2009 at 10:04 AM.
Good Performance .....BUT Amir Khan still ¨has a glass chin !!
One day he´ll go down like he did against Prescott... If he faces the likes of Ricky Hatton !!
By Steve Hughes.. Posted July 19 2009 at 7:54 AM.
Great fight khan and very well engineered. Mashallah and inshallah you would win more fights with the blessing of god. Good we need more British fighters to win and get the more belts.
By mohammad wahid chaudhry.. Posted July 19 2009 at 7:26 AM.
Well done Amir!!! You've done the nation proud. Superb performance and hope the haters and doubters out there recognise your talent. well done team Roach!!!
By dean.. Posted July 19 2009 at 1:10 AM.
Well Done Amir, a punch perfect display.
By Jono.. Posted July 19 2009 at 1:02 AM.