Dasaolu got off to a blazing start and charged to the line, becoming only the fourth British sprinter to beat 10 seconds as he clocked a time that is just 0.04 seconds slower than Linford Christie's British record of 9.87.
The 25-year-old Dasaolu, whose sole international medal is a silver in the 60m at the European Indoor Championships earlier this year, had a previous personal best of 10.03 seconds set just two weeks ago in the same city.
Saturday's semi-final run, which was wind assisted but not beyond the legal limit, is quicker than anything Usain Bolt has produced so far this year. Only Tyson Gay (9.75), Asafa Powell (9.88) and Justin Gatlin (9.89) have run quicker in 2013.
"I knew I was going to run quick from the first step," the Loughborough-based Dasaolu athlete told the BBC.
"Once you get to 60-70m, your body is running as quick as it can and it's all about relaxation. Because I was so far ahead it was much easier to relax."
Dasaolu then disappointed the crowd by pulling out of the 100m final, allowing Dwain Chambers to claim a seventh British crown with a time of 10.04.
The man of the hour had no regrets about not winning his national title, however, as he looks to the World Championships next month.
"My ultimate aim is to be fit for Moscow and I don't want to risk an injury competing in the final," he said.
"As a sprinter, you want to go underneath 10 seconds and I'm happy to do that.
"Sub-10 is a big thing for me and I just hope to continue running sub-10s. I'm happy with 9.91 and I just want to build on that.
He has become the second fastest British man of all time. The only other British sprinters to beat 10 seconds are Christie, Dwain Chambers (9.97) and Jason Gardener (9.98). Chambers did once match Christie's 9.87, but that run was removed from the record books due to his use of performance-enhancing drugs.
Dasalou clearly believed that he was set to put in a fast run this weekend, telling the Daily Telegraph that his career was set to take off after overcoming a string of misfortunes related to a new, lighter training schedule.
“I haven’t been injured now for 18 months since I made the move and started to do things differently,” said Dasaolu.
“The injuries I was getting were all different: hamstrings, calves, my foot. It was never anything specific. It was more about overloading in training.
“I always knew there was talent there. It was just about finding the right programme and the right person to manage it and make it happen. I never stopped believing but I needed to find the programme that worked for me.”
Though the Nigerian descendant ultimately withdrew from the final, his time is enough to take him to the World Championships.
"If you look at my season progression I knew a sub-10 was coming," said Dasaolu, who pulled out due to suffering with cramp. "We knew we were in a good place and I knew it was on the cards.
"It happened and I managed to record a personal best of 9.91 and it feels brilliant.
"I'm just happy to be one of the best sprinters in Britain. Going a sub-10 now gives me that confidence that when I stand with other sub-10 runners I know I can challenge them."
Chambers, now 35, will return to another World Championships and British sprinting - which has had some difficult times in recent years - finally appears on the up.
"That felt good and to be able to secure my spot was important," said Chambers.
"The major pressure is now off and we can just concentrate on keeping fit and healthy for the Sainsbury's Anniversary Games in London and for Moscow.
"I tried so hard (to dip under 10 seconds) this weekend. But, I had to be sensible and do the logical thing and qualify.
"For what it’ s worth, I think it’s fantastic that James (Dasaolu) has been able to do that time. It’s helped motivate me even further to want to run. It also bodes well for our relays."
Asha Philip ran the qualifying time to win the women's 100m title in a personal best 11.20 secs ahead of Anna Lewis and Desiree Henry, who one year ago was selected as one of the young athletes to light the London 2012 flame.
"An A standard, personal best and a win, I don’t know what more I could ask - everything was perfect," said Philip.
"Hopefully there’ll be another PB in Moscow. I’ve been running PB’s all year. I’ve been out for so long, so to come back injury free and run PB’s, it’s like the heavens have opened for me."
Tiffany Porter claimed the 100m hurdles title as expected in 12.68 secs while Chris Tomlinson took the men's long jump in the absence of injured Olympic champion Greg Rutherford - his winning leap 8.03m metres.
Meanwhile, Christine Ohuruogu, a world champion in Osaka five years ago, insists she is brimming with confidence after winning the 400m title.
"It feels nice to win domestically, now I can go tackle the guys abroad," she said.
"It is always a good field and sometimes when you’re so used to running the global events sometimes you can view the domestic events less highly but you always have to work hard regardless and never let your guard down."
- Sports & Recreation
- Athletics, Track & Field
- Dwain Chambers
- Linford Christie