MIAMI GARDENS, Fla. — Alex Smith, who threw three touchdown passes, was the obvious hero in the Kansas City Chiefs’ 34-15 victory over the Miami Dolphins on Sunday at Sun Life Stadium.

However, Frankie Hammond Jr. was the under-the-radar star.

Hammond made a pair of dubious decisions while fielding punts inside his own 5-yard line on Sunday, but one of those returns played a huge role in the Chiefs’ first win of the season.

“He probably should have let a couple of those go,” Chiefs Coach Andy Reid said of Hammond. “The flavor of the day, though, is that you are returning everything. Studies show that there’s production there.”

Two of Smith’s TD passes were to running back Joe McKnight, including a 4-yarder with 4:35 left in the game, capping a nine-play drive.

But it was Hammond’s 47-yard punt return — which he fielded at his own 4-yard line — that kick-started the drive.

Earlier in the game, a similar Hammond decision backfired. He fielded a punt at his own goal-line and ran it 48 yards. But a block-in-the-back penalty on the return forced the Chiefs to start the drive on their 1-yard line.

On the next play, Smith was sacked by defensive tackle Randy Starks and linebacker Jelani Jenkins for a safety, cutting the Chiefs’ lead to 21-15.

“It was a blitz up the middle,” Jenkins said. “They kind of had me blocked. I just kept moving my feet.”

That, however, turned out to be the Dolphins’ final points. The Chiefs scored the final two touchdowns, including a rather meaningless tally with 13 seconds left on a 6-yard run by running back Cyrus Gray.

In the end, Kansas City (1-2) snapped a five-game losing streak that dated to last season. The Chiefs’ most recent win before Sunday came Dec. 15 against the Oakland Raiders.

Smith made a couple of mistakes — a lost fumble and the safety — but he was efficient throwing the ball, completing 19 of 25 for 186 yards. He was not intercepted.

“This is what you are looking for,” Smith said, “a tough win on the road.”

Miami, which knocked off the New England Patriots in its season opener, fell to 1-2.

Dolphins quarterback Ryan Tannehill struggled. He completed 21 of 43 passes for 205 yards.

Wide receiver Mike Wallace led Miami with five catches for 74 yards, but there were seven incompletions on passes thrown in his direction. And, the Dolphins had no plays longer than 30 yards.

“Kansas City clearly deserved to win this game,” Miami coach Joe Philbin said. “It was a team loss in every respect.”

What the Chiefs said:

“I was talking to a specific section that I always used to mess with when I was a Dolphin. It was nothing negative. I couldn’t hear what they were saying, but I just told them that this was my house.” — Cornerback Sean Smith, on playing against his former team.

What the Dolphins said:

“It’s probably a drop here and a hold there. We are doing some things to ourselves that makes it more difficult.” — Wide receiver Brian Hartline, on the offense’s lack of production.

What we learned about the Chiefs:

1. Frankie Hammond Jr. is a dangerous punt returner. His 47-yarder set up the game’s most important touchdown. Earlier, he had a 48-yarder wiped out by a penalty. True, Hammond fielded both of those punts inside the 4-yard line, which is supposed to be a no-no. However, Chiefs coach Andy Reid said that the modern thinking on that play is changing. He said studies show there is value in returning punts from inside the 10-yard-line, and Hammond proved that on his 47-yarder. Even with the punt that got called back due to the penalty, Hammond returned five punts for 100 yards Sunday, a neat 20-yard average.

2. The Chiefs can function without running back Jamaal Charles. That is not to suggest that the Chiefs won’t be better once Charles returns from his ankle injury. After all, Charles led the league with 1,607 rushing yards last season. However, Knile Davis, who ran for 132 yards and a touchdown against the Dolphins, is proving to be a capable backup. Also, third-stringer Joe McKnight was a revelation Sunday with six catches for 64 yards and two scores.

–RB Joe McKnight was a revelation Sunday with six catches for 64 yards and two scores. McKnight also gained 65 yards on three kickoff returns. McKnight is still only 26. He showed flashes in his first three years in the NFL, all with the Jets. In 2011, for example, he averaged 31.6 yards per kickoff return, including one for a touchdown. He averaged 27.5 yards per kickoff return in 2012 before sitting out last season.

–QB Alex Smith threw three touchdown passes in the Chiefs’ 34-15 victory over the Miami Dolphins on Sunday. Smith made a couple of mistakes — a lost fumble and a safety — but he was efficient throwing the ball, completing 19 of 25 passes for 186 yards. He was not intercepted. It was a typically efficient Smith performance, one in which he checked down to running backs and found tight ends repeatedly.

–S Eric Berry, who sustained an ankle injury last week, did not play. CB Ron Parker moved to safety to fill the void.

What we learned about the Dolphins

1. Miami can have a running game without Knowshon Moreno. Despite losing Moreno to an elbow injury last week, the Dolphins still got 108 yards on 15 rushes from Lamar Miller, who averaged 7.2 per carry. Miller was also fairly effective in the passing game, catching four of the five balls thrown in his direction. However, those four grabs totaled just 24 yards, and Miller failed to get in the end zone all game. That fact — and the loss — took some of the shine off of Miller’s performance, but it still offers hope for the Dolphins.

2. The Dolphins’ front seven on defense showed considerable vulnerability. Even though the Chiefs were without their top rusher, Jamaal Charles, Miami allowed his backup, Knile Davis, to rush 132 yards and one touchdown. The Dolphins also allowed third-string running back Joe McKnight to catch six passes for 64 yards and two touchdowns, and Miami saw Chiefs backup tight end Travis Kelce catch three passes for 36 yards and a score. In fact, the Chiefs’ wide receivers inflicted very little damage. It was all about the running backs and tight ends.

–QB Ryan Tannehill struggled. He completed 21 of 43 passes for 205 yards and one touchdown. Tannehill was not intercepted, but he failed to come up with the big play when needed. He threw at least three balls that were deflected at the line of scrimmage, and his completion percentage was poor.

–WR Mike Wallace led Miami with five catches for 74 yards, but there were seven incompletions on passes thrown in his direction. His longest reception was for 30 yards, which isn’t bad … but it is not what the Dolphins expected when they signed him before last season. They thought they were getting a long-ball receiver, but Wallace has not had that kind of impact, mostly because he and QB Ryan Tannehill have not been able to find the right timing on deep throws.

–RB Knowshon Moreno (elbow) did not play against the Chiefs. Moreno rushed for 134 yards in his Miami debut, a Week 1 upset of New England, but he got hurt early in the Dolphins’ Week 2 loss at Buffalo.