Giroud came off the bench to net a second-half double in Dublin after first-half goals from Mason Mount and Emerson Palmieri had put the visitors in control.
Despite making 11 changes at half-time, Lampard – in just his second match as Chelsea boss following their midweek draw at Bohemians – will still have taken much from the friendly at Richmond Park as he gears up for the start of the new Premier League season next month.
Mount, who spent the previous campaign playing under Lampard while on loan at Derby, was handed a first start as the new manager fielded a strong-looking lineup, with the midfielder catching the eye with a neatly-taken opening goal after 14 minutes.
Lampard also began with a front two of Tammy Abraham and Michy Batshuayi, two other players recalled after being loaned out last season.
The Belgian forward impressed with a dynamic first-half display in which he was unlucky not to score, before Lampard changed both personnel and shape to a 4-2-3-1 in the second period, with the experienced Giroud leading the line.
And Giroud staked a claim to start away to Manchester United on the opening weekend of the season with two well-taken goals to complement a first clean sheet under the new manager.
With Chelsea currently under a transfer embargo, their new head coach was particularly impressed with how his youngsters performed in Dublin, especially the likes of Mason Mount, Tammy Abraham and Fikayo Tomori.
“Good performance, good result. We could have scored a lot more goals was the one thing I was slightly frustrated with. But I was particularly impressed with the energy of the team I the first half, which I was thought was great,” said Lampard.
“You have to put everything into these games to get something out of them. And the second half, I did not quite like as much and those are the things that show you need to keep working.
“Fitness is what we are striving for and combinations and we already have combinations with the ball, but our fitness can get much netter.
“A lot has been made of the younger players we have here and they need to know that if they impress and put what they did into a game like today’s, then great.
“From the first moments you could see that Mason, Tammy and Tomori were really at it and that is what we want. We need to have competition in the squad, we work hard here, the academy has been first class for years and we want those players to show they deserve a place in the team.”
Sky Sports News reporter Gary Cotterill was at Richmond Park to watch Chelsea in action and it was their England U21 international midfielder Mason Mount – among others – who really stood out for him.
“Mount was very lively, he took all the dead-ball situations and he looked full of confidence and someone who had been told he had a future at the club. He obviously only played the first 45 minutes, but was involved in a quite a lot of Chelsea’s best moves.
“Tomori was solid, quietly effective and did not do anything silly.
“Chelsea were much better in the first half than second and Giroud did was he does, taking a couple of chances. But in the first half, Batshuayi and Abraham linked very well together and also worked hard off the ball – which Lampard commented on after the game.”
“Batshuayi does have a reputation of needing four chances to score one goal and he was a bit like that today, but Lampard put that down to him being a bit rusty. But to me, he looked really keen and up for the battle and even chased one stray ball that was clearly going out for a goal kick. And it is that kind of attitude that Lampard wants and is after.
“I think Reece James – who is injured back at Chelsea currently – Mount, Tomori, Kurt Zouma, Batshuayi and Abraham will all stay at Chelsea next season.
“And a word about Lampard as at half-time, when they made 11 changes, it was him who was actually doing the warmups, not the coaches.”