Pirates 9, Cardinals 2: Pedro Alvarez hit a three-run homer and Francisco Liriano pitched seven strong innings as host Pittsburgh beat St. Louis in the opener of a five-game series.

Andrew McCutchen had a run-scoring single prior to Alvarez’s first-inning blast as the Pirates moved within a half-game of first-place St. Louis in the National League Central.

Liriano (11-4) struck out eight and allowed one run and four hits while winning for the sixth time in seven starts. The left-hander has given up two or fewer runs in seven of his last eight outings.

Pittsburgh had a 4-0 lead before St. Louis starter Jake Westbrook (7-5) retired his first batter. McCutchen drove in the first run with a sharp single to center before Alvarez slammed his NL-leading 27th homer over the right-field fence.

The Cardinals got on the board in the sixth when pinch hitter Tony Cruz tripled and scored on Matt Carpenter’s single to center. Pittsburgh responded with five seventh-inning runs on Gaby Sanchez’s sacrifice fly, Alex Presley’s single, Clint Barnes’ two-run double and a pinch-hit single by Starling Marte.

GAME NOTEBOOK: Alvarez is 13-for-23 with three homers and 11 RBIs against Westbrook. … Westbrook allowed four runs and four hits in five innings to drop his career mark against the Pirates to 1-8. … Pittsburgh placed C Michael McKenry (knee) on the disabled list and recalled Presley from Triple-A Indianapolis.