The old Matt Harvey was back for the New York Mets.

What was working for Harvey in the Mets’ 1-0 win over the Chicago White Sox on Monday?

The biggest key was that Harvey’s fastball was just about all the way back. The pitch averaged 95.8 mph last season and a season-high 95.5 mph on Monday. Entering the start, his fastball was averaging 94 mph this season.

The White Sox were 2-for-12 against Harvey’s heater, managing just a .167 batting average against it, which was the lowest in a Harvey start this season.

Harvey also got a 27 percent miss rate with the pitch, his highest rate of the season. In his previous three starts, his miss rate averaged eight percent. He got more missed swings against his fastball on Monday (7) than in those previous three starts (6).

Harvey’s four strikeouts with his fastball were one shy of his most in a game this season.

Mets manager Terry Collins offered strong praise of Harvey’s changeup and slider, calling the changeup his second-best pitch of the day. Harvey got five outs on the 10 changeups he threw, yielding no baserunners. In Harvey’s last start against the Nationals, he threw six changeups, yielding three hits, including two home runs.

He also got five outs with his slider without allowing a baserunner.

The 10 batters retired with his changeup and slider are his most in any start this season and his second-most in any start since the beginning of 2015.