Arsenal's Arteta praises Nketiah but laments not killing game against Forest
Goals from Eddie Nketiah and Bukayo Saka gave Arsenal a 2-0 lead but they took their foot off the gas in the second half which allowed Forest to strike back on a counter-attack through Taiwo Awoniyi to set up a frantic final 15 minutes.
"It's always difficult to win the first game in the Premier League. I think we deserved to win," Arteta told TNT Sports.
"But we didn't kill the game and 2-0 in the Premier League is a really dangerous result. We had a lack of concentration on the counter after the corner, they scored a goal and then it's game on and they throw a lot of bodies there.
"We didn't concede anything but the feeling was, 'Okay, we want the game to end and (take) the three points'."
With Arsenal cruising at 2-0, Forest boss Steve Cooper sent on Anthony Elanga and Awoniyi, with the pair combining for the goal.
"You cannot give anything and today we gave them some hope and we gave them the goal. And when that happens against teams in the Premier League, you cannot do that," Arteta added.
"This team is so well organised, so competitive. They are so physical when they want to be and they don't need much to score a goal."
However, Arteta praised Nketiah, saying he had earned his place in the starting line-up in training after failing to make the cut for their Community Shield win over Manchester City.
"He is a clear example of what we're going to need this season, a player that was very disappointed because I didn't start him against Manchester City," Arteta said.
"What he did was came on in that game, had a huge impact against City, trained like a beast this week, telling me 'I deserve to play'. So I had to play him because he gave me every reason with a reaction to play.
"And when that happens, you come to the pitch and you score and you play the way he's done. So great example."
Arteta said, though, that Nketiah would still have to earn his place again when they play Crystal Palace in their next game.