They led 18-4 until going down to 12 men in the final stages and conceding two late tries.
“I was really proud of it,” said Agar, whose injury-hit side remain in the hunt for the play-offs.
“I thought it was spirited and committed. Huddersfield are a tough team to break down and after the initial exchanges, it was a game we dominated for long periods.
“I am not sure how we ended up with only six points difference on the scoreboard.”
Like Leeds, Huddersfield were missing a raft of first-team players and their coach Ian Watson felt Rhinos’ experienced stand-off Robert Lui was the difference.
“We were beaten by the quality of Rob Lui,” he said.
“We’ve a lot of guys learning in that position. We’re a tough team to beat but we’re getting beat at the moment through our naivety.”
Giants were supposed to see stand-off Lee Gaskell, 30, return from an ankle injury.
But Watson said: “We had to send him for a scan at five ‘o clock. He had 10 weeks of rehab’, trianed with the team this week, had no reaction but last night had some kind of reaction. He would have massively helped.”