"Very dissatisfied,'' interim manager Jim Riggleman said. "Very happy with the intensity and effort we get from our guys every day, but 3-6 is not acceptable. But that's what we did, so we have to accept it and move on."
Maybe heading home will aid the Reds as they start a six-game run in Cincinnati on Tuesday against the Rockies. However, the Reds have won 11 games on the road and nine at home.
"It's always great to be at home,'' Riggleman said. "Being at home seems to help and certainly we have to play good baseball when we get home."
Cincinnati brought the tying run to the plate with two outs in the ninth against reliever Kirby Yates. But Joey Votto grounded out on a checked swing to end the game. Votto had three of the Reds' 12 hits.
Castillo (4-6) was cruising along until the fifth, denying the Padres a runner in scoring position. But the right-hander got in a jam by allowing a single to Franmil Reyes, a bunt hit to Freddy Galvis and a walk to Manuel Margot.
After Raffy Lopez bounced into a forceout at the plate, Hunter Renfroe produced the 12th pinch-hit grand slam in Padres history. When Castillo's 81 mph elevated sinker reached the middle of the plate, Renfroe didn't miss it. His blast ricocheted off the Western Metal Supply Co. Building's second deck to give the Padres a 4-2 lead.
"I was focused on getting a ground ball to turn a double play, but sometimes things don't go the way you want to and he hit a homer,'' Castillo said through a translator.
It was the first pinch-hit slam allowed by the Reds since the Mets' Ike Davis hit a walk-off one on April 15, 2014, against J.J. Hoover.
When Hosmer got his third hit two batters later, Castillo was replaced by David Hernandez. Castillo worked 4 2/3 innings and was charged with four runs, six hits and a walk. He struck out three in losing his second consecutive start.
The Reds went up 2-0 in the fifth on Scooter Gennett's RBI single, which brought in Jesse Winker, who was aboard on a single. Cincinnati might have had a bigger inning but after Billy Hamilton led off with a walk, he was cut down by Lopez when trying to swipe his 11th bag.
SOUND SMART Riggleman returned to familiar turf in San Diego this weekend, as he served as the Padres' skipper from 1992-94. Riggleman is one of 14 managers to work for at least five Major League teams. His other stops were with the Cubs, Mariners and Nationals.
HUGHES IS NO ZERO Jared Hughes blanked the Padres over 1 2/3 innings of relief. The right-hander hasn't given up a run in his last 12 appearances to stretch his career-high scoreless streak to 15 1/3 innings.
"He has really been a great acquisition for us,'' Riggleman said. "He's had a lot of days off here lately and there was a possibility he would be rusty, but he was really sharp. He's just been a pleasure. He wants to pitch, he loves to pitch. Whether winning, losing tied, save situation, non-save, he wants the ball.''
HE SAID IT "We got 102 ballgames left and we got to win a whole bunch of them. When we have a lot of stretches like 3-6, you are not going to win a whole bunch of them and it's not acceptable." -- Riggleman, on what lies ahead for the Reds
UP NEXT Right-hander Anthony DeSclafani makes his season debut on Tuesday after an oblique strain placed him on the DL on March 29. DeSclafani, who went 9-5 with a 3.28 ERA last season for the Reds, will square off against lefty Kyle Freeland of the visiting Rockies to kick off a three-game series. First pitch is at 7:10 p.m. ET.
Jay Paris is a contributor to MLB.com based in San Diego.