Gerrard, returning for Liverpool after a complicated groin injury, struck with a 68th-minute free kick that went through the defensive wall after Rio Ferdinand had tripped Charlie Adam just outside the penalty area.
Hernandez, who came on as a 76th-minute substitute for Phil Jones, then nodded the ball into an empty net from point-blank range with nine minutes to go after Danny Welbeck had flicked on a corner.
United stayed top of the table with 20 points from eight matches, at least until Manchester City host Aston Villa later on Saturday. Liverpool remained fifth with 14 points.
“It wasn’t the best free kick,” Gerrard told Sky Sports. “I tried to get it over the wall but I got a bit of luck.
“To come back and play my first full 90 minutes today … growing up these are the games you dream of playing in and when you are sitting in the stands there is nothing worse, to be out there experiencing the emotions again was fantastic.”
United defender Ferdinand, who has also had a spell out injured, said: “It was great to be back and after losing here for the last three visits I’m pleased we’ve left with a point.”
The visitors started without Wayne Rooney, Hernandez or Nani up front. They played five men in midfield and made little impact on the Liverpool defence, failing to have a worthwhile shot on target until the closing stages.
Liverpool, buoyed by the return of Gerrard who had made three previous substitute appearances this season, had more possession and looked more dangerous as the match wore on and went close to a winner several times in the final minutes.
Rooney, who was handed a three-match ban for Euro 2012 by UEFA on Thursday following his England sending-off against Montenegro last week, came on for the last 20 minutes but made little impact.