Cardiff City manager Steve Morison told BBC Sport Wales: "We weren't good enough, we got the goal and could have had another one but we didn't do enough today, it was not a good enough performance.
"Last week we were brilliant, this week I can only apologise to the 2,000 odd fans who gave up their Saturday to come and watch us not turn up.
"We're only two games in, there will be a level of inconsistency because things take time... it's a very even league but it is unforgiving, and if you're not at it you will get beat."
Reading manager Paul Ince said: "I'm delighted. We were disappointed with the Cardiff goal but this group don't give in and the response was brilliant, we put them on the back foot.
"It was a disappointing decision from the referee [not to send off Nelson]. I don't want to see people get sent off but it baffles me. If you miss big decisions, it could have cost us. These things change games. It's a blatant red. It's crystal-clear.
"This team is always going to fight and the Championship is about competing. I thought the fans were brilliant and they understand the situation we're in. This is where we are and today we got what we deserved."