The British and Irish Lions have Sonny Bill Williams in their sights in the second Test against the All Blacks in Wellington on Saturday as they battle to keep the series alive.
With the Lions on the ropes after being crushed 30-15 last weekend in the first of the three-Test series, Gatland announced a rejigged side for the rematch and singled out the code-hopping Williams as one player they had to stop.
"It's important we shut him down," Gatland said after entrusting the 94 kilogram (14st 11lb), 1.80 metres (5ft 11in) Owen Farrell with marking the much bigger Williams who weighs in at 108 kilos and stands 1.91 metres tall.
"We allowed him too much time on the ball last week. I can't remember Sonny Bill passing the ball during the game but he got some good gain line and a couple of offloads away and gave them front-foot ball.
"We have to make sure of our line speed in terms of stopping that. It is important that we stop that and have been working hard on that all week."
The bruising Ben Te'o, entrusted with marking Williams a week ago, had been hailed as one of the standouts of the tour but is now a casualty from the first Test fallout.
In a previous life, playing the rival rugby league code, Te'o may have claimed the upper hand when he frequently clashed with Williams but all that changed when it came to a rugby union showdown.
He tried to assert his authority with a crunching tackle early in the second half only to be penalised for driving Williams illegally into the ground while the double World Cup winning All Black centre picked himself up and continued unscathed.
Gatland said it was tough to drop Te'o, who will get time off the bench, "but we made a call based on the opportunities we created and think we stretched the All Blacks at times".
The decision to move Farrell to inside centre has allowed Gatland to start Johnny Sexton at fly-half to have dual playmakers in action.
It indicates a change of emphasis for the Lions after the All Blacks negated their standard rush defence and box kick tactics in the first Test.
Gatland, who has toyed with pairing the two pivots Farrell and Sexton in earlier tour games, said the combination "does open some opportunities for us if we do get the ball back to attack and that is why we have gone with the combinations we have."
"From an attacking perspective it has given us more of an attack with the 10-12 combination.
"It just gives us two ball players, two kicking options. A first and second receiver and we have two left foot options with Jonathan Davies and Elliot Daly as well."
British and Irish Lions Team
15 Liam Williams, 14 Anthony Watson, 13 Jonathan Davies, 12 Owen Farrell, 11 Elliot Daly, 10 Jonathan Sexton, 9 Conor Murray, 8 Taulupe Faletau, 7 Sean O’Brien, 6 Sam Warburton (captain), 5 Alun Wyn Jones, 4 Maro Itoje, 3 Tadhg Furlong, 2 Jamie George, 1 Mako Vunipola.
Bench: 16 Ken Owens, 17 Jack McGrath, 18 Kyle Sinckler, 19 Courtney Lawes, 20 CJ Stander, 21 Rhys Webb, 22 Ben Te’o, 23 Jack Nowell.