Gurriel, Thomas hit 3-run homers, D-backs beat Cubs 6-4 in showdown of NL wild-card contenders

Lourdes Gurriel Jr. and Alek Thomas hit three -run homers for the Arizona Diamondbacks .

Rookie Brandon Pfaadt delivered 5 1/3 quality innings for the D-backs.

Cubs ace Justin Steele gave up six earned runs on seven hits and two walks over six innings.

All-Star Marcus Stroman was activated from the 15-day injured list.