PITTSBURGH (AP) - Like most of his brethren, Chicago Cubs manager Rick Renteria is getting a handle on Major League Baseball's expanded replay system.
And just like everything else with the perpetually rebuilding club, the learning curve is steep.
The Cubs were on the wrong side of two replay reviews in Monday's 1-0 opening loss to the Pittsburgh Pirates, including an overturned call in the top of the 10th that allowed Neil Walker to hit a game-ending homer off Carlos Villanueva in the bottom of the inning.
Chicago's Emilio Bonifacio singled with one out in the top of the 10th and was ruled safe when he dived back to first on an attempted pickoff by reliever Bryan Morris.
Pirates manager Clint Hurdle trotted out to challenge the call, which was overturned by replay officials in New York.
''I'm still trying to figure out what the `clear and convincing evidence' is supposed to be,'' Renteria said. ''It's a work in progress. They have a lot of people looking at those videos in New York, so they must get it right.''
The largest regular season crowd in the 14-season history of PNC Park (39,833) roared when Bonifacio was ruled out and the din only grew louder when Walker smacked a Villanueva (0-1) changeup into the right field seats.
''This one feels pretty special,'' Walker said. ''This is a special day for this team, this organization. We've come a long way.''
Walker's first career game-ending homer easily cleared the Clemente Wall while his teammates rushed onto the field in celebration. It was the first opening-day walkoff homer for the Pirates since Bob Bailey's off San Francisco's Juan Marichal in a 1-0 victory in 1965.
Bonifacio went 4 for 5 for Chicago, but the Cubs were 0 for 11 with runners in scoring position and wasted a fine start by Samardzija, who scattered five hits over seven innings.
''I was happy with the way I kept the ball down in the strike zone,'' Samardzija said. ''It helped to get the double plays because they made the overall outing look a little better than it really was.''
Travis Ishikawa had two of the six hits by Pittsburgh, which began 2014 much the same way the Pirates spent a long stretch of their breakout 2013: by riding solid pitching and a lights out bullpen to victory.
Pittsburgh starter Francisco Liriano resurrected his career last season, winning 16 games despite not making his first start until May and putting together a pair of solid postseason outings.
Vaulted to opening-day starter after the offseason departure of A.J. Burnett, Liriano looked comfortable as an ace and didn't panic when he got into trouble. He worked out of a two-on, no-out jam in the fifth thanks in part to a double play upheld on video review that served as the debut of MLB's expanded replay.
Renteria challenged a double-play following a demonstrative ''safe'' call by Samardzija following a poorly executed sacrifice bunt attempt. First base umpire Bob Davidson's decision was confirmed on replay.
''We already were in the fifth inning,'' Renteria said. ''If he's safe, we're first and second, so I thought it was time to give ourselves the opportunity to get a call.''
Samardzija proved every bit Liriano's equal, striking out three and walking two before giving way to a bullpen that had little trouble until Walker stepped in leading off the bottom of the 10th.
NOTES: Though the left-handed Ishikawa started in the opener, Hurdle reiterated Gaby Sanchez will get the majority playing time at the position and the manager does not see the left-handed Ishikawa and the right-handed Sanchez working on a straight platoon rotation. ... Pirates C Chris Stewart took batting practice and says he is coming along ahead of schedule in his rehab from knee surgery. Stewart believe he can beat the timetable of late April for his return. ... Chicago OF Brian Bogusevic was unavailable because of ankle soreness. He is expected to be ready to play Wednesday. ... The teams are off Tuesday. Chicago's Edwin Jackson faces Pittsburgh's Charlie Morton on Wednesday night.