Meanwhile, British number one Elena Baltacha will face Slovenian seventh seed Tadeja Majeric in the women’s singles final on Sunday.
Baltacha, 29, who won the Aegon Nottingham Challenge crown in 2011, will feature in her first decider since undergoing foot surgery last year after easing past Italian fourth seed Nastassja Burnett 6-0 6-4.
“It is quite amazing really, I’ve not played for nine months and I just feel it is my tournament,” Baltacha said.
“I can't put it into words how happy I am to be in this final - especially in Nottingham, a place which is very special to me as this is my third final here.”
The Aegon Team GB star blitzed the world number 136 by taking the first set in 23 minutes.
Burnett started brightly in the second and broke the Scot early. But it was just the first twist, as neither one of them managed to hold their serve in four successive games.
Baltacha eventually composed herself to go 5-4 up, and then broke the right-hander for the third time in the set to seal the win.
The Scot was quick to pay tribute to her support staff for getting her to the final.
“All the work I have done with Nino (Severino), Louie (Cayer), Ben Haining and Alisdair Jones feels like it is paying off,” Baltacha said.
“Alisdair has played a massive part in my recovery. I did my rehab with him, and he is with me this week which has been so important. This morning I was feeling a little bit battered and Alisdair really came to the rescue and patched me up.”
Elsewhere, Majeric brought qualifier Miki Miyamura’s remarkable run to the last four to an abrupt end with a 6-0 6-4 win.
The world number 135 suffered an early exit in the Aegon Trophy at the same venue a week early, beaten by Briton Tara Moore.
The Slovenian’s form reversal was clear as fought her way past second seed and Aegon Trophy champion Petra Martic in Friday' quarter-final.
In the men’s final, Johnson fought back from a break down in both sets to overcome the Ruben Bemelmans of Belgium 7-5 7-5 in less than 90 minutes.
It is Johnson’s second ATP Challenger tournament win and first outside of America after he claimed his maiden crown in Aptos, California, in 2012.
Johnson knew that victory at the Nottingham Tennis Centre could see him follow Australian Matthew Ebden, who claimed the Aegon Trophy at the same venue six days earlier, into Wimbledon.
“It means a lot to me. It is only my second tournament on grass and to come here and win it, play five good matches like I did and beat a player like Ruben is special,” Johnson said.
“That was a tough final, and to start with I felt I was fighting myself a little bit – I was uptight and nervous, it is my first grass court final, there were a lot of points and stuff on the line that people may not realise.”
Johnson said he was suffering from the fatigue of his first European campaign during the Aegon Trophy, as he bowed out in the second round to eventual finalist Benjamin Becker who then went on to the quarter-finals of the Aegon Championships as The Queen’s Club.
Now, the big-hitting American hopes to capitalise on his surge of form on the biggest grass stage of them all.
“Last week I was feeling a little tired and fried, and now to come out here and put a week together like this gives me a lot of confidence going into Wimbledon,” Johnson said.
Bemelmans, who looked in control of proceeding when serving for the first set at 5-4, praised Johnson for his combination of power on the forehand and momentum swinging slice game.
“I played well today, but Steve has a really big forehand and he puts a lot of pressure on you - once you are under pressure it is tough to get out,” Bemelmans said.
"I was feeling well and playing well, I was up in both sets. It was unfortunate for me as he played great on all the big points - all credit goes to him.”
Aegon Nottingham Challenge results – Saturday 15 June
Men’s singles - Final
S Johnson (USA) d R Bemelmans (BEL) 7-5 7-5
Women’s singles – Semi-finals
E Baltacha (GBR) d  N Burnett (ITA) 6-0 6-4
 T Majeric (SLO) d [Q] M Miyamura (JPN) 6-0 6-4
- Sports & Recreation
- Aegon Trophy
- Elena Baltacha
- Tadeja Majeric