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CINCINNATI -- Of all the Reds rookies to reach the big leagues this season, the growth and improvement of left-handed starting pitcher Brandon Williamson has been the most dynamic while also being the most under the radar.

“I think it’s just realizing how to throw to guys," Williamson said. "Really, it’s as much mental as it is physical. If you can execute the pitch that you want, then it becomes a chess game of ‘Just how do you move the pieces?’ And I feel like that has been a big step since I got up here.”

Williamson's best two starts of 2023 have been his most recent. Although he pitched only 5 2/3 innings for a no-decision during Sunday's 4-2 loss at Pittsburgh, he allowed one earned run and two hits. After a leadoff single in the first inning, he retired 12 in a row and 14 of the next 15.

On Aug. 7 in a win over the Marlins, Williamson delivered 6 2/3 innings with one earned run, three hits, no walks and nine strikeouts.

“It’s probably the best start of my life, honestly," he said.

The Reds acquired Williamson as part of the March 14, 2022, trade that sent Jesse Winker and Eugenio Suárez to the Mariners. Jake Fraley, Connor Phillips and Justin Dunn also came to Cincinnati in the deal.

Williamson didn't have a robust year in 2022 at Double-A and Triple-A and had a 2-4 record with a 6.62 ERA in Louisville when the Reds called him up to fill a hole in their rotation. He was still inconsistent in his early starts after his May 16 big league debut at Colorado and his status to remain seemed initially tenuous.

How did Williamson put himself firmly in the Cincinnati rotation?

An improved fastball is one of the biggest reasons.

Take a look at Williamson's splits below:

GS W-L ERA BAA Fastball Velocity

May and June 8 1-1 5.82 .263 92.3 mph

July and August 7 3-1 2.98 .191 93.5 mph

Then there is Williamson's cutter, also much improved.

May and June: 25.2% usage, 88.1 mph, .371 BAA, .686 SLG

July and August: 30.3% usage, 89.9 mph, .135 BAA, .243 SLG

Williamson was trying to pound the pitch inside to right-handed hitters early on this season but often ended up leaving it out over the plate. Here is the May and June heat map of that pitch from Statcast:

In July and August, Williamson was targeting the cutter to righties up and away more.

Williamson credited much of his improvement to working with pitching coach Derek Johnson.

"He’s been very specific and forward with what is expected and what needs to change," Williamson said. "It’s how we can get better doing it. The uptick in velocity is directly correlated to working with him. I think throwing more strikes is correlated with him. My body feels great, that was a big component last year when I was struggling. I didn’t feel like myself physically or mentally. Now I feel really free on the mound. I know more of how the game works and how big league hitters think and work. I’m never shy of throwing the ball over the plate right now. I’m attacking guys.”

As he trends upward, Williamson has managed to combine development as a pitcher with having good performances at the big league level, which is no easy feat.

“We’ve known he can pitch," manager David Bell said. "This is a big jump to this level. It took him a little bit to settle in, and he just keeps getting better and better, more comfortable. And he’s just really pitching the way he knows he’s capable of and it has been good enough."