Marmion was drafted into Irish training in Monaghan on Friday after Conor Murray sat out the heavy session due to a groin injury and, in turn, the Connacht scrum-half was rested for their clash with Dragons on Saturday.
Marmion, who was 25 last week, has chalked up all but one of his ten caps off the bench, with both of his Six Nations appearances coming as a replacement against Italy this season and a year ago.
“He trained all week but then he got called into Irish camp on Thursday night,” said Lam.
“We had a big training run on Thursday and then he drove maybe three hours to Monaghan on the Thursday night because Conor Murray wasn’t able to train and then they had quite a big session yesterday.
“He drove back late Friday night. When Joe told me I said great that he got up there. I said to him, we are blessed to have three good half-backs, so I said to Kieran let’s make a call on it and see how you come in.”
Lam said that when they did their matchday tests on Saturday morning, Marmion’s scores were ‘a bit low around some of his legs’, so they decided not to risk him.
“He was keen to play but ultimately he was feeling a bit sore, a bit tired. But I made the call what’s best for Ireland, what’s best for Connacht and what’s best for Kieran. Now Marmion should be fresh for next week.”
His replacement Caolin Blade made the most of the opportunity, sniping over for their second try after 14 minutes, with Craig Ronaldson’s conversion making it 14-0.
Earlier, Jack Carty and Matt Healy to send Tiernan O’Halloran away for the opening try after five minutes, with the Connacht full-back showing that he, too, is in flying form if the opportunity for his Six Nations debut arises.
That early burst should have seen Connacht push on and claim a bonus point but their play disintegrated and an error-strewn display — the sort which has been alien to the home fans in the Lam era — left them hanging on for the win in the end.
Dragons clawed their way back into it, an Angus O’Brien penalty after 18 minutes making it 14-3 at the break, and two more from the Dragons’ replacement out-half in the third quarter ensured a nervous finish for Connacht.
“We are all obviously disappointed but it goes to, go back to work on Tuesday and go through and make sure we have got the learnings from it,” added Lam.
“We had a good week and we were certainly a lot better than we have been. Defensively that was probably one of our best in terms of the percentages we had.”
Tries: O’Halloran, Blade; Cons: Ronaldson (2).
T O’Halloran; N Adeolokun, T Farrell, C Ronaldson, M Healy; J Carty, C Blade; D Buckley, D Heffernan, F Bealham; U Dillane, Q Roux; S O’Brien, J Heenan, J Muldoon.
T McCartney for Heffernan (57), J Cooney for Blade (57), N Fox-Matamua for Dillane (63), J Cannon for Roux (69), R Parata for Ronaldson (77), R Loughney for Buckley (78), JP Cooney for Bealham (78).
Pens: O’Brien (3).
T Prydie; A Hughes, T Morgan, A Warren, P Howard; D Jones, T Knoyle; S Hobbs, E Dee, B Harris; N Crosswell, R Landman; O Griffiths, N Cudd, L Evans.
A O’Brien for Jones (15), C Hill for Landman (40), T Davies for Hobbs (60), L Fairbrother for Harris (60), S Beard for Warren (68), H Keddie for Griffiths (77), S Pretorius for Knoyle (77).
Nigel Owens (WRU).