In a span of two days, the White Sox’s rotation has gone from suspect to arguably the second-best group in the AL Central.The main reason is the team’s reported agreement Saturday on a three-year, $55.5 million contract with free-agent left-hander Dallas Keuchel. Keuchel’s addition comes one day after the Sox signed free-agent left-hander Gio Gonzalez to a one-year pact that also includes an option for 2021. Keuchel’s deal reportedly includes an $18.5 million vesting option for 2023. The Sox’s rotation still trails the Indians, even though Cleveland traded former ace Corey Kluber earlier in December. The Tribe boasts Mike Clevinger (another trade target), Shane Bieber, Zach Plesac, Adam Plutko and Aaron Civale. Plutko’s 97 ERA+ was the worst of the group in 2019.Keuchel, who will turn 32 on Jan. 1, helped fill a need in the Braves’ rotation last season after signing a prorated one-year, $20 million with the club in June. He wound up making $13 million with Atlanta. Keuchel posted a 3.75 ERA (4.72 FIP) in 19 starts for the National League East champions. He also made two starts in the Braves’ NLDS vs. the Cardinals but totaled just eight innings pitched.His addition to the South Siders is also another clear sign that the White Sox believe their window of contention has opened. Chicago has added catcher Yasmani Grandal (free agent) and right fielder Nomar Mazara (trade) this offseason to complement Yoan Moncada, Eloy Jimenez, Tim Anderson and Jose Abreu in the lineup. Chicago also has highly regarded prospects Luis Robert (center field) and Nick Madrigal (second base) waiting in the wings. SPRING TRAINING 2020: Reporting dates for pitchers, catchersChicago will begin 2020 with Keuchel, 2019 breakout star Lucas Giolito, Gonzalez and developing right-handers Reynaldo Lopez and Dylan Cease as its top top five. Even if you take out Lopez and Cease, who posted ERAs of 5.38 and 5.79, respectively, last year, Chicago’s top three stacks up favorably with the division champion Twins’ top three of Jose Berrios, Jake Odorizzi and Michael Pineda.