"We had a bit of trouble getting out of our own half, something we've done well in the last three games," Smith said.
"The Highlanders put a lot of pressure on the set piece and the tackled ball.
"We knew that was going to happen but we just didn't deal with it and we gave away a lot of penalties that we shouldn't have."
The lead changed hands during a game that was marked by solid defence from both sides and saw only two tries.
Barrett landed four penalties to go with Cory Jane's five-pointer for the home side, while Slade scored a try, converted it and added three penalty goals before Noakes finished the job.
In what was the first home game of the season for the Hurricanes after they opened their campaign with a three-leg road trip, Smith said they wanted to perform in Wellington.
"It was a pretty excited group. We were coming home. We knew that people would recognise there was a bit of ability in the group, and some of the newer boys especially wanted to prove themselves," Smith said.
"Sometimes you just try too hard and things don't come off. A few passes were being thrown and on another day you'd keep hold of the ball and then you'd make ground the next play. Things like that were what brought us unstuck a few times.
"We didn't play well. We're better than that and we're just going to have to prove that in the weeks to come."
The Highlanders became the first team this season to win their opening four games and are one of only two unbeaten teams in the competition alongside the Stormers, who have played only three games.
"We got off to a great start," Highlanders' captain Jamie Mackintosh said.
"We're a bit more of an experienced team and we wanted to put pressure on them but they did really well to come back into the game.
"I think we dominated field position in the second half and we were just inches from scoring a couple of tries to put them away.
"But in the end we played some real composure footy in the right bit of the field, so four wins makes us happy but obviously it wasn't easy as well."
The Highlanders next meet the Brumbies in Canberra on Saturday night.
Highlanders 19 (Colin Slade try; Slade con, 3 pens; Chris Noakes pen) Hurricanes 17 (Cory Jane try; Beauden Barrett 4 pens) HT: 14-13.
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