Khan wins by a unanimous points decision
Khan retains WBC Silver welterweight title, wants fight with Mayweather next
Khan has now won 30 of 33 fights, Alexander 26 of 29
Fight took place at MGM Grand, Las Vegas
GET INVOLVED: Best British pound-for-pound boxer in last 20 years #bbcboxing
Image source, Getty ImagesIt has already been a sensational night for London-based Andy Lee, who has clinched the vacant WBO world middleweight title.
The 30-year-old, who represented Ireland at the 2004 European Championships, won the belt with a sixth-round stoppage victory against previously-unbeaten Russian Matt Korobov.
Lee has now won 34 of 36 fights, with 24 of those victories coming inside the distance.
Alexander is already looking frustrated with a shake of the head in the third round as Khan's quickness is again causing the American problems. A perfect start for Khan, who has probably taken all three opening rounds. Quick, fast and hard from an excellent Khan so far.
We asked who is the best pound-for-pound British boxer over the last 20 years. Here are some of your answers from the BBC Sport Facebook page., external
Lee Ifans: Joe Calzaghe. His record speaks for itself.
Image source, AFPMichael Williams: Hands down Lennox Lewis. Anyone who says Khan knows nothing about boxing.
Jamie Rossiter: Ricky Hatton and Carl Froch for excitement. Lennox Lewis and Joe Calzaghe for legacy. Difficult to pick just one.
Amir Khan's trainer Virgil Hunter tells his man after the opening round 'don't get wild, stick to the plan'. It is an impressive start from the British boxer, who looks too quick for his opponent, with Alexander unable to get his jab working.
But then a right-hand from Alexander stings Khan, to remind him he might not have it all his own way.
Image source, Fight LabelAmir Khan's shorts feature white leather, silk and a 24-carat gold thread waistband
Not only does Amir Khan want to impress in the ring in Las Vegas, he wants to look the part inside and out of it as well - by wearing boxing's "most expensive shorts".
The shorts, made of white nappa leather, silk and featuring a waistband made of 24-carat gold thread, are reported to be worth at least £20,000. Sheffield company Fight Label, who made the shorts, said Khan "wanted extravagant and we've delivered".
Sophie Whittam, who designed the shorts, told BBC Radio 5 live: "I think it's possibly the most expensive shorts ever made.
"We worked closely with Amir's team. For around four to six weeks we've been working on designs and colours and obviously Amir and his family had a little bit of input, but at the end of the day it's what we think is going to look best. It is a very involved process."
Amir Khan has already shown his quick hands with a powerful combination in the opening minute of the contest as he looks to unsettle his opponent.
That flourish is as good as the round gets. But the Brit, the more aggressive, has probably done enough to take the opener.
Former super-middleweight world champion Joe Calzaghe on Twitter:, external Good to be back in Vegas. Looking forward to the big fight tonight I go for Khan points win.
Calzaghe, who won all 46 of his professional fights, defeated American Bernard Hopkins on a split decision in Las Vegas in April 2008.
Image source, Getty ImagesAnd here we go...
But where does Amir Khan go next if he wins today and does not get a bout with Floyd Mayweather?
Well, what about sharing the ring with Sheffield's unbeaten Kell Brook, the IBF welterweight champion. Brook certainly is keen.
Image source, Getty ImagesHe said: "Carl Froch's fight with George Groves at Wembley was massive. And this could be another packed Wembley fight in the summer.
"Khan has only had one fight at welterweight and doesn't deserve a fight with me - he doesn't deserve a shot. But everywhere I go people say 'when are you going to fight Amir Khan'. Forget egos, we should just sign the contract and make it happen. It's a fight everyone wants to see."
The talk in the build-up has been that Amir Khan may fight Floyd Mayweather Jr, if the Brit beats Devon Alexander.
Well, Mayweather has thrown a curve-ball into the mix in the last few hours by saying he is interested in fighting Philippines' Manny Pacquiao, an eight-weight world champion. However, a bout between these two has been repeatedly talked about for years and never materialised.
Image source, AFPBut in an interview with Showtime Boxing, Mayweather said: "I would love to fight Manny Pacquiao - we're trying to make the fight happen. Floyd Mayweather is not ducking or dodging any opponent. Now it's time for us to talk, we want to fight. Let's make it happen. May 2, let's do it."
The fighters are in the ring and Jimmy Lennon Jr announces the fighters to a packed crowd at the MGM Grand. "It's showtime," screams the excited ring announcer.
Image source, PALas Vegas has become a second home for Amir Khan in recent years. Four of his last six fights have taken place there. His first three came at Mandalay Bay, but now he has returned to the amazing MGM Grand, the venue for his points victory over Luis Collazo in May.
Anyone who has been there will know the hotel is a huge maze, where you spend hours unsuccessfully trying to find your hotel room so decide to head to one of the numerous bars, restaurants, casinos or nightclubs instead.
British fans will certainly not be short of options for things to do there. But now is not the time to visit the lions enclosure and the Cirque du Soleil show can wait for another night. Tonight, the action comes from the 16,800-seat Grand Garden Arena, nestled in the bowels of the building.
So Floyd Mayweather is regarded as the best pound-for-pound boxer in the world, but who is the best British pound-for-pound boxer over the last 20 years?
Also, send us your thoughts on Amir Khan and his fight against Devon Alexander tonight.
Get involved on Twitter, using the hashtag #bbcboxing, leave a message on the BBC Sport Facebook page or text us on 81111 (UK only) and we will post the best messages on this page.
Image source, BBC Sport
Image source, Getty ImagesWill those comments come back to haunt Devon Alexander?
The man in the opposite corner tonight is 27-year-old American Devon Alexander, a former two-weight world champion.
Image source, Getty ImagesAlexander, with 26 wins and two defeats from his 28 professional contests, has held the IBF and WBC titles at light-welterweight, before moving up to welterweight.
He is looking to get back to the top of the division after losing his IBF world welterweight belt to Shawn Porter last December.
We have already mentioned that Khan has set his sights on a potential showdown with Floyd Mayweather Jr.
But any hopes of fighting the American, who is unbeaten in 47 fights and the current holder of the WBC World welterweight, WBA Super World welterweight and WBC World light middleweight titles, will be smashed to pieces if Khan loses in Las Vegas.
And it is not going to be easy for the 28-year-old from Bolton.
Hello and good morning. Whether you're bleary eyed after setting your alarm clock for an early start, or just coming in after a fun Saturday night out, thanks for joining us and welcome to BBC Sport's live text commentary on what could be a huge night in the career of Amir Khan.
"I want the boxing fans around the world to demand a fight between me and Floyd Mayweather."
Image source, Getty ImagesBritain's Amir Khan holds the WBC Silver welterweight title, but is not satisfied. What he wants more than anything is a shot at the unbeaten American, regarded as the best pound-for-pound boxer in the world.
Image source, Getty ImagesKhan fights today in the gambling capital of the world.
A stunning, impressive victory, could just lead to him hitting the boxing jackpot.