"That's a glimpse of what we can do," Blackmon said. "We've got playmakers here. We know it. We've just got to go out there and finish games."
Blackmon caught his first pass of the year for a 67-yard score after serving a four-game suspension. He had five receptions for 136 yards.
Cecil Shorts III caught a 4-yarder from Chad Henne early in the fourth that cut the gap to a touchdown.
Pettis got away from Will Blackmon on the clinching score to cap an 80-yard drive. His 4-yard TD catch at the end of the first half finished a 12-play, 90-yard march to make it 24-10.
Darian Stewart set up a touchdown with a forced fumble and fumble recovery in the second quarter. James Laurinaitis intercepted Gabbert in the end zone in the third quarter to keep the Rams up by 14.
Joeckel was hurt when a Rams lineman rolled under him on a run. Joeckel was the second pick in this year's draft and started at left tackle after Eugene Monroe was traded to Baltimore for multiple draft picks.
Robert Quinn helped set up Giordano's interception when he got a piece of Gabbert on the pass rush. Gabbert stepped up but overthrew Blackmon, and Giordano threaded his way across the field to tie it at 7 late in the first quarter.
Gabbert was 2-0 at the Edward Jones Dome in college, helping Missouri beat Illinois twice in his hometown. He's 5-22 as the Jaguars' starter.
In a span of four plays early in the second quarter, the Rams tied it on a short field goal by Greg Zuerlein and capitalized on a turnover to take their first lead. Stewart stripped Clay Harbor after a short reception and returned the fumble 19 yards to the Jacksonville 16, and Lance Kendricks stretched for the pylon on the next snap.
The Jaguars totaled eight points in the first half all season before busting out with 10 in the first quarter. Blackmon's TD was their longest play of the year.
Jones-Drew had 70 yards on 17 carries and is the third Jaguars player to top 10,000 yards.