Trailing by 4 points with a little more than six minutes left in the game, backup quarterback Sean Mannion methodically marched the Los Angeles Rams up the field and connected with rookie Josh Reynolds for the decisive touchdown in a 24-21 preseason win on the road over the Oakland Raiders on Saturday night.

Mannion connected with Mike Thomas on a quick slant to keep the drive alive while facing fourth and 9 from the Raiders' 37-yard line. On the next play, he sailed a 20-yard pass up the sideline to Reynolds, the long, athletic fourth-round pick, who beat out fellow rookie Chris Humes for the football with just over a minute remaining. The Rams' offense looked good late, but was even more impressive early on.

Here are some notes on what stood out.

QB depth chart: Jared Goff put together what was quite possibly the most encouraging performance of his short NFL career. He finished 16-of-20 for 160 yards and a touchdown, with several impressive throws throughout the night. Goff led the Rams to two touchdowns and a field goal before exiting. His only real mistake was waiting too long to deliver a deep ball to an open Robert Woods, instead absorbing a sack from Khalil Mack. Besides that, Goff was exceedingly accurate and decisive. Mannion had another good day in relief of Goff, going 15-of-22 for 132 yards and a touchdown. That follows last week's strong performance against the Cowboys, when Mannion was 18-of-25 for 144 yards.

When it was starters vs. starters, the Rams looked ...: Like a well-oiled machine on offense. When's the last time you read that? They went 6-for-8 on third down, picked up 12 first downs and consistently marched the ball up the field. Cooper Kupp made six catches (on seven targets) for 70 yards and a touchdown, and was wide open for a 23-yard catch on play-action to start the game. Todd Gurley, meanwhile, ran violently, with eight carries for 38 yards and a touchdown, on a 2-yard run up the middle. The Rams' defense -- which was without key players like Robert Quinn, Mark Barron, Kayvon Webster and Nickell Robey-Coleman -- was shaky, allowing a couple of touchdowns to Oakland's Derek Carr-led offense.

One reason to be concerned: Splitting hairs here. The Rams' secondary got off to a rough start, though Webster, Robey-Coleman and Mike Jordan were all held out. On the Raiders' first touchdown drive, Lamarcus Joyner committed two personal fouls in a span of four plays. On the Raiders' second touchdown drive, Amari Cooper made a leaping catch despite triple coverage, and Michael Crabtree juked Troy Hill for a touchdown. The Rams did, however, get an interception from their primary corner, Trumaine Johnson, who grew up in nearby Stockton, California, and had upwards of 70 people in the stands.

That guy could start: Justin Davis won't unseat Gurley as the featured running back, but the undrafted rookie is making a legitimate case to crack the roster, which is impressive in itself. Davis fumbled twice in the preseason opener, but he also gained 70 yards on nine carries. Davis picked up only 8 yards on five carries against the Raiders, but he gained another 20 on three catches and once again looked shifty with the ball in his hands. A knee injury has kept Lance Dunbar from practicing. And though Malcolm Brown has been used as Gurley's backup, Davis may be forcing his way into the conversation.

Rookie watch: Kupp had another great showing. His best catch came on a quick slant, on which he was well-covered for a throw that sailed low and away. It was his fourth third-down reception, perhaps a sign of things to come. Tight end Gerald Everett made four catches for 30 yards, with one of those resulting in a 24-yard gain thanks to a nice cutback in space. Defensive lineman Tanzel Smart, who has impressed this summer, did a nice job of bringing down E.J. Manuel after he tried to escape the pocket. And Casey Sayles clinched the win with a sack.

Watkins watch: New receiver Sammy Watkins made his Rams debut, wearing No. 2, his number from Clemson, which he will have to change for the regular season. Watkins caught a 5-yard pass to convert on third down and also gained 3 yards on a screen. Watkins then ran a fly route in hopes of connecting with Goff downfield, but a well-placed throw near the end zone was broken up.

Injury report: Thomas absorbed a helmet-to-helmet hit by Anthony Cioffi while hauling in Mannion's fourth-down throw near the middle of the field with about two minutes remaining. Thomas was checked on by Rams trainers and walked off on his own power. Backup outside linebacker Carlos Thompson had to be carted off the field after sustaining what appeared to be a significant injury to the lower part of his left leg. Raiders rookie offensive lineman Kareem Are launched himself toward the pile near the midway point of the fourth quarter, but instead caught Thompson's knee.