Reja's men extended their unbeaten run in the Serie A to six matches, yet to taste defeat in the league since the Italian returned to the helm at the start of January.
He was happier with his side's first half than their second, but was pleased to secure a point against the league's second-placed team.
"In the first half we did very well, creating a lot of problems for them down the flanks," Reja told Sky Sport Italia.
"After the break they held more possession but we held out in defence and allowed them few chances.
"We had some promising counter-attacks that we didn't make the most of, especially an incredible chance with Eddy Onazi.
"At a certain point Roma pinned us back but the lads held firm and I am content with the draw."
Stefano Mauri made his Lazio return when he was brought on at half-time for his first appearance since May 2013 after a six-month match-fixing ban.
Reja expects the 34-year-old to get better with more match practice.
"Francesco Totti and Daniele De Rossi were causing us problems, as De Rossi was often left alone, so I had to block these players off," Reja said.
"Mauri is not at 100 per cent yet but he just needs to play in order to get there."
Reja apologised to opposition coach Rudi Garcia after jokingly suggesting he hoped a Roma player got injured before the derby.
"I apologised both publicly and privately with Roma. I did my duty and my CV speaks with not just numbers but also behaviour, so I feel the reaction was a little over the top," he said.
"It was not my objective to make barbed comments."
