Colombian-born Vargas had already been put down himself when he stunned Khan and the capacity crowd and with Brook watching at ringside, Khan recovered and floored Vargas again before eventually running out unanimous points victor. He had not been taken 12 rounds since a points win over Chris Algieri in May 2015.
Now, however, with Khan looking to once again re-establish himself as a top contender with a win over Samuel Vargas on Saturday, talk has already turned to whether Brook might just be the next name on the Bolton-born fighter's list.
"When it was first announced, I actually thought that Khan would beat Kell" Nelson told iFL TV.
Both fights would gross an estimated £20 million, according to promoter Eddie Hearn, with Khan likely to earn nearer £12 million for the fight with Brook, with Las Vegas and the Millennium Stadium, Cardiff, both options in December.
Khan locks horns with Samuel Vargas in Birmingham tonight.
Vargas always felt he had a punchers chance but that was about it to be honest and Khan rightly had his hand raised after a fight which raised as many questions as it did answers for the future of one of the countries most famous fighters. "Kell wants the fight and I know Amir will fight him".
Talking about his future plans, he said: "The only fight that works for me over Kell Brook is Manny Pacquiao".
The Colombian was not seriously hurt and in the fourth caught Khan with a right hand. The bell arrived to save Khan, who scored another knockdown in the third before the pace gradually slowed.
But Vargas, who was stopped by Garcia in seven rounds two years ago and in four rounds by Spence in 2015, stubbornly fought back and breached Khan's defense early in the seventh round.
"Kell is the don when he is stronger, but I actually think Khan could beat Kell at welterweight".
The former light-welterweight world champion, who had dropped Phil Lo Greco twice in under 39 seconds, was given a much sterner test by Vargas.
He was up quickly but was immediately sent staggering backwards again amid more lightning Khan combinations.