ENGLEWOOD, Colo. -- The most fascinating part of Monday's OTA session came when the Broncos worked in a series of fourth-down situations, with one repetition for each of the first, second and third units from the 24-yard line, 20-yard line, 12-yard line and 6-yard line.

"I really liked that -- last plays of the game, fourth down," tight end Jeff Heuerman said. "It's good work. It's good stuff to do during the spring."

... In the battle of No. 1 units, the defense got the better of matters, stopping the first-team offense on each of the four plays. The high points for the defense came from plays snapped at the 12- and 6-yard lines, as Case Keenum looked for Hamilton and Heuerman, respectively, but were felled in part by string coverage from Justin Simmons and Shaquil Barrett on DaeSean Hamilton and Will Parks on Heuerman.

Parks' coverage set up a situation where Keenum had a tiny window near the left sideline in the end zone. Keenum succeeded at squeezing the ball in there, giving Heuerman a chance, but he couldn't quite reach the football.

Safety Jamal Carter's interception was the highlight of the second-teamers' duel. With the offense at the 24-yard line, Lynch looked down the middle for Kenny Bell, who caught a handful of passes from the third-year quarterback throughout Monday's practice. But safety Dymonte Thomas arrived to deflect the football at the goal line, allowing Carter to pounce and fall to the ground for the touchback.

After an incompletion on an end-zone attempt to tight end Matt LaCosse from the 20-yard line, Lynch hit running back Dave Williams in the left flat on his play from the 12-yard line. At full speed and with full contact, Williams might have been able to bull his way to the goal line; in an OTA without pads, the play was dead before he reached the end zone. On the last repetition for the No. 2 offense, the pass rush collapsed the pocket, preventing Lynch from getting off a throw before the whistle blew.

... The Chad Kelly-led offense scored twice in its four plays against the No. 3 defense, thanks in part to some outstanding work from the wide receivers. On the play from the 24-yard line, Kelly lobbed a pass to the back of the end zone that rookie John Diarse caught behind the defense. He made the leaping grab and got both feet in-bounds for the score.

Kelly looked for Diarse again from the 20-yard line, but tight coverage from Zaire Anderson ensured the pass fell incomplete. From the 12, Kelly hit Jordan Leslie on a slant route with three defenders in the area for a touchdown. The defense rebounded by forcing a stop from the 6-yard line, as rookie safety Trey Marshall forced LaCosse to run out of real estate in the back of the end zone, leading to a pass that sailed out of play.

Diarse said that Kelly's presence in the huddle has helped when he's guided the offense.

"[He's] somebody I can lean on," Diarse said. "I have questions, and I have somebody I can confide in when a defense doesn't look right. He's doing a great job of leading us in that huddle."

Other practice observations: Keenum wasted no time adjusting to the collection of young wide receivers he had at his disposal for Monday's OTA.

With Demaryius Thomas and Emmanuel Sanders not taking part in the voluntary session, rookies Courtland Sutton and DaeSean Hamilton moved up to the first-team offense. Isaiah McKenzie worked in the slot.

On the first snap of the initial team period, Keenum found Hamilton. Three plays after that, Keenum turned to his right and hit Sutton.

"We didn't miss a beat," Head Coach Vance Joseph said. "That's what you want from your backup players. Someone's not here today, they step in and play. We don't miss a beat. So I was very impressed with those three guys, including Isaiah McKenzie, who played slot today."

Hamilton was involved throughout practice. The work wasn't perfect; Hamilton dropped a pass at one point. But Keenum kept looking in his direction, and Hamilton recovered from the drop for back-to-back receptions later in practice.

"It helps us see what he's seeing when we go out there and we're really running routes for him, practicing with him and building that chemistry. Case has done a great job, especially today," Hamilton said. "[It was great] taking first team reps and being out there with him, understanding what he likes, understanding where he expects us to be and really just the anticipation of where he's going to place the ball."

... Diarse showed the depth of the rookie receiver class by catching another touchdown pass late in practice, leaping for a grab from Kelly in the back of the end zone during the final team period.

However, the undrafted rookie from TCU downplayed his accomplishments.

"That's just doing your job and exceeding expectations," Diarse said. "It's the NFL. Every ball in the air has to be caught. We have to dominate as receivers to take advantage of every opportunity we get, and that was just one that you just don't think about, and you go after [it]."

He left Monday's work wanting more.

"I can do better," said the undrafted rookie from TCU. "I hold myself to a higher standard. Obviously those are good plays to make, but the expectation level is high, so I have to meet those expectations."

... The Broncos got some no-huddle work in midway through the practice, which provided another chance for the offense to take advantage of its simplified verbiage.

"I think it's just the ability to have us go out there and play fast," running back Devontae Booker said. "The play-calling, it gets in quick. There's not any long plays. Once the play [is] called in the huddle, we know what it is, everybody [gets] aligned, [and we] just go out there and play fast."

During the two-minute period, Keenum and Lynch guided the first- and second-team offenses into scoring range.

Lynch got his drive going by scrambling out of pressure from defensive end Shelby Harris to run for the first down. He moved the chains again on passes to River Cracraft and Carlos Henderson, advancing the offense to the defense's 13-yard line before the march stalled.

On the final play of Keenum's drive, he caught his own pass and ran for what could have been a first down in a game situation. Defensive end Adam Gotsis swatted the pass at the line of scrimmage, but then Keenum adeptly caught it and scooted 5 yards upfield on the fourth-and-5 play.

Keenum completed passes to Heuerman and Isaiah McKenzie to start the drive, with the completion to McKenzie stopping the clock as he went out of bounds after the reception.

... RB De'Angelo Henderson was held out of team repetitions because of a strained oblique muscle. He participated as well as he could, jogging through routes on the sideline during some snaps of the team period to mimic the role he would have if he was in action.

... With Henderson sidelined, rookies Royce Freeman and Dave Williams saw more extensive work. Freeman had one of the best runs of the day, cutting back to his left through a solid hole and bursting for what could have been a run of 20 or more yards in a game.

... Rookie linebacker Keishawn Bierria made a play in coverage, getting his hands on a Kelly attempt as he dropped into space.

... Quarterback Nick Stevens got his first team-period work of OTAs on Monday, hitting rookie running back Philip Lindsay on his first attempt.

"The coaches have told me that once we get all the installs in is when I'm going to start getting some team reps sprinkled in here and there," Stevens said. "I just have to take advantage of those opportunities."