SANTA CLARA, Calif. -- The newfound, fast-break offense of the San Francisco 49ers was on full display in the first half of their preseason opener against the Houston Texans.

Those opening 30 minutes gave a glimpse of the good and bad that can come with coach Chip Kelly's preferred up-tempo approach. On the plus side, there was the dominant running game that surely brought a smile to Kelly's face and a 43-yard touchdown pass from quarterback Blaine Gabbert to tight end Vance McDonald. On the other side of the coin was a pair of fumbles, one of which was scooped up and returned for a touchdown while the other occurred inside Houston's 5-yard line.

That 14-point swing prevented the Niners from taking a big early lead on the way to a 24-13 preseason loss. The first half offered the best barometer for where the Niners are at this early stage of the preseason. It was in those opening two quarters that San Francisco played its starters and primary backups.

Chip Kelly's fast-paced offense amassed more than 300 yards in the first half against the Texans, although a pair of fumbles proved costly. John Hefti-USA TODAY Sports

When it was all said and done, the 49ers had outgained Houston 302 yards to 89 and run a whopping 50 plays to Houston's 25 in the first half. Of those 302 yards, the Niners amassed 161 on the ground at an average of 7.7 yards per carry. To put that all into context, the 2015 49ers averaged 60.6 offensive snaps for 303.8 yards and 96.5 rushing yards per game.

"Chip doesn’t really share the science behind it, we just go out and try to execute as quickly as we possibly can," McDonald said. "It opens things up for the offense and that’s really the value of his offense. I thought we executed really well. There were a couple of really bad things turnover-wise, which was an ugly part of the game that really set us back. In terms of tempo, I thought we did well.

“When you look at ballgames in the last year, we were 52 total (plays) throughout the whole four quarters. Yeah, it’s really fun. I knew this offense, going into the first preseason game, would open things up. It was just fun to get out there and let loose and wear the defense down.”

That fatigue factor seemed to work best in the running game, where the Niners were able to rip off seven runs of 13 or more yards. A couple of those were quarterback scrambles rather than designed runs, but the point still stands that for Kelly's offense to rev at its best, the run game needs to be at the center of it.

"We’re running a fast tempo, but we’re running downhill like you saw today," guard Joshua Garnett said. "We’re running in between the tackles. We’re running some outside zone stuff. We’re still going to run downhill and we want to get vertical, which is something that a lot of people don’t think that we really do, just because it’s so high tempo or so Oregon-oriented. But we are running downhill like you saw today."

With the running game working, the Niners were able to keep their foot on the gas and dictate the pace to Houston. But when it wasn't working, the Niners found themselves behind the sticks and off the field. Combining short three-and-outs with turnovers is one of the worst things that can happen to a defense.

“You kind of saw, when you go three-and-out, what it can do," Gabbert said. "When we get rolling and string together a bunch of quality plays and have extended drives, it puts such pressure on the defense to make plays. When we’re rolling like that, you can call any play and we’re going to make it work.

“It was fun to get out there and get our feet wet in this system. Games are a lot different than practice and to see the tempo that we can play at, to see the level that we can execute at when we are rolling. There’s definitely some good things on that film. But like I said earlier, there’s a lot of ups and downs and definitely things that we can correct from the film and that we will going into next week.”