Mektic and Pavic have won seven titles on tour this season but are looking for their first at a Grand Slam. They had to come from two sets down to beat Lukasz Kubot and Marcelo Melo in the quarterfinals.
Granollers and Zeballos beat Simone Bolelli of Italy and Maximo Gonzalez of Argentina 6-4, 6-4, 7-6 (3) in the other semifinal.
Granollers and Zeballos beat Mektic and Pavic in the Madrid Open final in May.
Eighth-seeded Karolina Pliskova reached her second Grand Slam final after rallying to beat No. 2 Aryna Sabalenka in three sets at Wimbledon.
In a matchup of two big servers playing in their first Wimbledon semifinal, Pliskova won 5-7, 6-4, 6-4.
Sabalenka saved all eight break points she faced in the first set — including four at 5-5 — and then converted her first when Pliskova double-faulted on set point.