Aaron Naughton (five goals) was the focal point in attack as Bontempelli and Ed Richards did plenty of the midfield grunt work in the Bulldogs' 13.8 (86) to 9.16 (70) victory at Marvel Stadium on Sunday.
Bontempelli shone with 25 disposals and 12 clearances, and kicked two crucial goals in the third term, which sparked the Dogs after West Coast had threatened to cause a boilover.
No.1 draft pick Willem Duursma sprinted away from opponents and kicked a stunning goal from inside the centre square to put the Eagles 14 points up.
But Bontempelli replied almost immediately from similar range and added a second soon afterwards when he worked off Duursma at a stoppage, wresting back momentum for the Bulldogs.
"They were critical goals and he's done that from time to time, hasn't he?" Beveridge said.
"I thought our leaders, definitely our captain and our vice-captains in Naughton and Richards, were exemplary in their performances.
"They had a real say in the end on the outcome."
Young gun Harley Reid's brilliant snap gave West Coast a three-point lead early in the final term, but the Bulldogs finished full of running.
The home side kicked 4.0 to 1.5 in the final quarter, including two late Naughton goals that helped seal a result that lifted the Dogs (10-7) to seventh on the ladder.
Richards finished with 28 touches, six clearances and one goal, with Bailey Dale (29 disposals), Rhylee West (23) and Tom Liberatore (23) also important contributors.
Reid had 27 disposals and nine clearances for West Coast and Duursma (20 touches) was busy in the middle, while Jobe Shanahan kicked two goals.
But a fifth consecutive defeat left the Eagles (4-13) in the bottom three.
"It's definitely disappointing to lose," Eagles coach Andrew McQualter said.
"I thought today was a winnable game for us and we gave ourselves a great chance to win, but accuracy hurt us in the end.
"It was an arm-wrestle for the majority of the game and it became a game of just taking your moments.
"The Doggies probably just did that a little bit better than us in the end."
Brandon Starcevich was one of the Eagles' best in defence despite suffering a cut under his eye and having his left ankle accidentally stepped on by Rory Lobb in a nasty-looking incident.
