The visitors' took as long as Juan Mata goal in first half injury-time to register their first shot on target and, despite Frank Lampard extending his side’s lead, a number of squandered chances allowed Adam Le Fondre’s last-gasp double to steal a share of the spoils for the relegation-threatened side.
“We are surprised because we were controlling the game for 85 minutes,” he told reporters.
“For the last free kick we made too many mistakes in one situation where we were doing well for 85 minutes. We had chances to kill the game; we didn’t take them and we paid for it.
“The main thing is we could have scored three or four goals and finished the game. We can say that we have to be more clinical.
Chelsea’s defence struggled to defend set-pieces throughout the game, notably hesitation inside the penalty area for Reading's 95th-minute leveller, and Benitez has urged more focus in future.
The result leaves the Blues 13 points behind leaders Manchester United, and the interim boss was also keen to stress that further lapses in concentration will only negatively affect the team’s fortunes.
“We have to be aware of these mistakes defending set-pieces,” he added.
“But I was really pleased with the players; for 85 minutes they were doing a great job. But these things make a difference. We could have two more points.
“We’re still in a very good position in the table but it could be even better.”