WASHINGTON -- The Nationals raised questions last month when they executed what was effectively a swap of their No. 4 starter. First, they traded Tanner Roark to the Reds at the Winter Meetings. Then they replaced him two weeks later by signing Anibal Sanchez to a two-year deal, with a team option for 2021.

The moves added a few million dollars of extra financial flexibility for the Nationals in 2019, which should help in their ongoing pursuit of a second baseman, while giving them a pitcher who likely has a higher upside for next season. But it's risky to move on from a stalwart to a lesser-known quantity, unless the Nats are extremely confident in their new acquisition.

They may have reason to be.

Sanchez had a resurgent 2018 season, but he will turn 35 in February and carries a spotty injury history. And before last year, he had simply not been very good for three seasons. From 2015-17, Sanchez struggled to stay on the field (averaging 23 starts) or to pitch effectively when he did take the mound (5.67 ERA). Roark, on the other hand, took the ball for at least 30 starts and 180 innings in each of the past three seasons, even if he had been slightly below league average the past two years.

So why are the Nationals placing their bets on Sanchez? Well, perhaps his 2018 season was no fluke. There are signs of a late-career second wind.

Sanchez was a master at generating soft contact last season, holding opposing hitters to an exit velocity of 83.7 mph, the lowest among pitchers who allowed at least 200 batted balls, to go along with a 25.8 percent hard-hit rate, the lowest allowed by any of the 210 pitchers who surrendered 100 batted balls, according to Statcast™. He induced weak contact 68.5 percent of the time last season, the sixth-best mark among starting pitchers with at least 200 batted balls allowed.

When Sanchez is at his best, he has been good at inducing weak contact. But last year, he made some significant changes in his pitch mix to do so.

Sanchez's arsenal has always made him unique. Last year, Statcast™ tracked him throwing seven types of pitches -- a sinker, four-seam fastball, cutter, split-finger fastball, slider, curveball and changeup -- each of which breaks in a different way. Of all the pitchers Statcast™ has tracked since its inception in 2015, Sanchez joins Mat Latos in '16 as the only two to throw seven pitches more than 5 percent of the time during a single season.

Sanchez has thrown a variation of seven pitches for years, but it was not until he started mixing them more effectively in 2018 that he started getting his desired results again.

Sanchez's sinker had been unremarkable, so he cut its usage from 23.4 percent in 2017 to just 7.8 percent in '18, while upping the usage of his cutter from 7.3 percent in '17 to 20.2 percent last year. The tradeoff worked well. Statcast™ tracked opposing hitters batting just .206 with a .357 slugging percentage against his cutter. The year prior, they had hit .311 and slugged .561 against his sinker. Sanchez also reduced the number of times he threw his slider (12.4 percent in '17 compared to 4.8 percent in '18), and it became a much more useful pitch (.471 batting average in '17 to .174 last season).

Sanchez has also made some tweaks to his fastball and changeup, which did not feature much separation in velocity early in his career. In 2011, his four-seamer averaged 92.3 mph and his changeup 87.7 mph. In '18, his fastball averaged 90.4 mph compared to 71.1 mph on his changeup. The results were stellar a year ago for Sanchez's changeup, which yielded an .088 batting average against, the lowest among 194 pitchers who had at least 30 plate appearances end in a changeup.

"I just prepared for my games better," Sanchez said last month. "I see that it's not important for me to throw harder, because I can locate better. And my changeup took the players off balance most of the time. That helped me to get the season that I wanted last year."

The more prudent decision for a team short on starting pitching depth would almost certainly have been to add Sanchez and keep Roark, so the Nationals may still regret shipping Roark to Cincinnati. But there are plenty of reasons to think the Nats may receive an upgrade from the No. 4 spot in their rotation next season.

It is a bit of a gamble, but one Washington was comfortable taking. The quartet of Max Scherzer, Stephen Strasburg, Patrick Corbin and Sanchez could form one of the best starting staffs in the National League.