A win in Santa Fe would make it three straight successes for Wales on their summer tour, with Gatland opting for dual opensides in his bid to tame the South Americans.
James Davies and Ellis Jenkins both begin the game, with Cory Hill remaining as captain.
"We have had another very good training week in Buenos Aires and we are ready to go for this game," said lock Hill, who has skippered Wales in their last two matches.
"Argentina are going to be coming for us, but we are ready for that challenge and it's the last game of the season for us so the boys are buzzing to get out there.
"We know we have six to eight weeks off after this so it's a case of one last effort and I'm sure the boys will put the hard yards in. A first series win here since 1999 is all the motivation we need."
Head coach Gatland has made five changes to his side from the one which downed Argentina 23-10 in impressive fashion in San Juan.
There are first starts of the tour for scrum-half Aled Davies and tighthead prop Tomas Francis, while Owen Watkin replaces the injured Hadleigh Parkes at inside centre.
Rhys Patchell has edged Gareth Anscombe for the fly-half jersey.
Scarlets flanker James Davies was man of the match against the Pumas in the first Test and hopes his partnership with Jenkins can drive Wales to victory.
The energetic openside said: "To put Argentina to bed in their back garden in the first Test was pretty pleasing and as a team we produced a really good performance.
"It's great to have competition. It keeps you on your toes in training and when you get your chance, you've just got to take it. The boys have been taking their chances well.
"The challenge is to back it up week in, week out. I've known Ellis for a long time and hopefully the combination of having two opensides works. Results are the key for everyone in this group.
"It's not about man of the match accolades or anything like that."
"It's an old school football stadium and it's going to be nice and hostile," Hill added of the Estadio Brigadier Lopez, which is surrounded by a moat and barbed wire.
"It's a great venue for us to play in. Three wins from three would turn this from a good tour into a great tour, but having a moat around the pitch is new to all of us!
"The boys are still loving the experience of playing in Argentina. The last time we won here Rob Howley and Neil Jenkins were the stars. They're our coaches now, so it was a long time ago!
"I'm sure they'll give me stick for saying that, but as a team I think we've got another five or 10 per cent more to give which is hugely exciting."
Pumas head coach Daniel Hourcade has responded to the 23-10 defeat in San Juan by making just the one change, Martin Landajo replacing Gonzalo Bertranou at scrum-half.
"We decided to select Martin and give the same team the chance again because none of them was happy with what happened last Saturday. We want a rematch," Hourcade said.
"We had a very bad game last week and we really want to reverse it. We are going to see a team with a lot of attitude and a lot of fire with desire to change the image we left in San Juan.
"The key is to change our attitude. We have to win the point of contact and put into operation the game plan we did not manage to do last week."
James Davies and Ellis Jenkins both begin the game, with Cory Hill remaining as captain.
"We have had another very good training week in Buenos Aires and we are ready to go for this game," said lock Hill, who has skippered Wales in their last two matches.
"Argentina are going to be coming for us, but we are ready for that challenge and it's the last game of the season for us so the boys are buzzing to get out there.
"We know we have six to eight weeks off after this so it's a case of one last effort and I'm sure the boys will put the hard yards in. A first series win here since 1999 is all the motivation we need."
Head coach Gatland has made five changes to his side from the one which downed Argentina 23-10 in impressive fashion in San Juan.
There are first starts of the tour for scrum-half Aled Davies and tighthead prop Tomas Francis, while Owen Watkin replaces the injured Hadleigh Parkes at inside centre.
Rhys Patchell has edged Gareth Anscombe for the fly-half jersey.
Scarlets flanker James Davies was man of the match against the Pumas in the first Test and hopes his partnership with Jenkins can drive Wales to victory.
The energetic openside said: "To put Argentina to bed in their back garden in the first Test was pretty pleasing and as a team we produced a really good performance.
"It's great to have competition. It keeps you on your toes in training and when you get your chance, you've just got to take it. The boys have been taking their chances well.
"The challenge is to back it up week in, week out. I've known Ellis for a long time and hopefully the combination of having two opensides works. Results are the key for everyone in this group.
"It's not about man of the match accolades or anything like that."
"It's an old school football stadium and it's going to be nice and hostile," Hill added of the Estadio Brigadier Lopez, which is surrounded by a moat and barbed wire.
"It's a great venue for us to play in. Three wins from three would turn this from a good tour into a great tour, but having a moat around the pitch is new to all of us!
"The boys are still loving the experience of playing in Argentina. The last time we won here Rob Howley and Neil Jenkins were the stars. They're our coaches now, so it was a long time ago!
"I'm sure they'll give me stick for saying that, but as a team I think we've got another five or 10 per cent more to give which is hugely exciting."
Pumas head coach Daniel Hourcade has responded to the 23-10 defeat in San Juan by making just the one change, Martin Landajo replacing Gonzalo Bertranou at scrum-half.
"We decided to select Martin and give the same team the chance again because none of them was happy with what happened last Saturday. We want a rematch," Hourcade said.
"We had a very bad game last week and we really want to reverse it. We are going to see a team with a lot of attitude and a lot of fire with desire to change the image we left in San Juan.
"The key is to change our attitude. We have to win the point of contact and put into operation the game plan we did not manage to do last week."
