Jose Mourinho praised the "big soul" of his Manchester United side in their 2-2 draw with Arsenal but bemoaned costly errors.
After a positive opening by United, David De Gea allowed Shkodran Mustafi's header to slip through his hands, with Ander Herrera failing to clear in time on the line.
Arsenal's second goal saw Marcos Rojo try desperately to make up for his error in giving the ball to Alexandre Lacazette only to slide in and score an own goal.
United responded quickly both times, with Anthony Martial grabbing the first equaliser before a calamity at the back for Arsenal allowed Jesse Lingard to nip in and level only 13 seconds after Rojo's own goal.
Mourinho was forced into a number of changes by his ever-growing injury list, particularly in defence. He selected Chris Smalling and Eric Bailly despite neither being fully fit while Rojo made his first appearance of the season and Diogo Dalot his first ever start in the Premier League.
Mourinho said: "Maybe we feel frustrated with the result, we feel frustrated with some mistakes, we feel frustrated with some moments where a little bit more quality would be needed but we have to be happy with the spirit, we have to be happy with the effort, the dynamic, the intensity.
"The team had a big soul. We scored four goals and we drew 2-2. Even in matches like today where we play well, we always shoot ourselves.
"But good performances. I could speak about everyone. Especially in moments where we are not very happy with the result, we need happiness on the pitch."
Mourinho dropped Paul Pogba and Romelu Lukaku to the bench, with both coming on in the second half, but denied the team's level of happiness was improved by neither being in the starting line-up.
He said: "I think Paul came on and gave a good contribution. I brought freshness and power to the attacking players but our defenders were dead. That made it more difficult to keep that happiness for the 95 minutes.
"In the last part of the game it was Arsenal wanting the draw, diving, getting the game stopped."
Mourinho reserved special praise for 19-year-old Dalot, who showed plenty of attacking intent down the right.
"The kid Diogo, fantastic," added the United boss. "I think Gary Neville must be thinking now that Manchester United has a right-back for 10 years."
Martial limped off during the second half but Mourinho offered a positive assessment, describing the Frenchman's problem as a "pre-injury" after he felt tightness.
There is likely to be far less positive news for Arsenal defender Rob Holding, who was carried down the tunnel on a stretcher after twisting his knee awkwardly and he may have suffered ligament damage.
Gunners boss Unai Emery said: "It's the worst for us today. Rob Holding, we are going to wait for the doctor but maybe it's a big injury."
Aaron Ramsey also had to be replaced but Emery described his problem as a small injury.
The Arsenal boss felt his side were unfortunate not to come away from Old Trafford with three points for the first time since 2006 in the Premier League.
He said: "I am very proud for our work and how we responded in the 90 minutes. When we are winning it was a good moment but they equalised very quickly then we got up after their two goals.
"In the second half our players worked to find a way to win. I think we were close, more than them, to do the third goal but De Gea saved two or three times with good action."