OAKLAND – For the first time in the history of interleague play, the Giants and A’s met on the field as last-place teams Monday night.

In the Battle of the Basement, the Giants bullpen sank to the bottom.

Giants manager Bruce Bochy tasked his relievers with protecting a one-run lead while recording a dozen outs. They never came close. George Kontos served up a grand slam to Marcus Semien in the sixth inning – a mistake that vaporized a decision for Matt Cain as the Giants lost 8-5 at the Coliseum.

The Giants continue to find ways to plummet without hitting bottom. They fell percentage points behind the Phillies for the worst record in the major leagues, and they wore it convincingly. The Giants’ four relievers combined to issue six walks and allow six earned runs in three innings.

The Giants and A’s are always playing for pride and local bragging rights, which mean something to the people who bang drums, paint their faces and – a true test of loyalty – brave the bridge traffic. There are few stadium sounds in Bay Area sports as unique as the mix when A’s fans boo Giants fans for cheering Buster Posey.

The A’s fans cheered loudest in the sixth, and the Giants were left again to reminisce what times were like with a functional bullpen.

The Giants led 3-2 because Cain was able to settle down after a rocky first inning and a bottom of the lineup that the Giants didn’t anticipate fielding in the spring scraped together a pair of RBI hits in the fourth. Jae-gyun Hwang singled home Posey, and Carlos Moncrief, a 28-year-old minor league journeyman making his first big league start, created a difference-making souvenir. He hit a hopper off the mound for an infield single – the first hit of his career — that scored Brandon Crawford.

But a Giants bullpen that blew two leads Sunday night at Dodger Stadium was even less reliable against a last-place opponent.

It’s hard to know what source of aggravation bothers Manager Bruce Bochy and pitching coach Dave Righetti more: the leadoff walks or the two-strike mistakes.

Josh Osich did some of both when he couldn’t put away Bruce Maxwell while putting him on base to start the sixth. After a lineout, pinch hitter Rajai Davis hit a double over the head of left fielder Gorkys Hernandez. Osich pitched carefully with a base open to Matt Joyce but yanked his full-count slider to load the bases.

Then Kontos left a 1-1 sinker over the plate to Semien, who cranked it over the fence in left-center.

The Giants rallied in the seventh for a pair of runs on four hits, showing some alert baserunning while going first to third on singles three times. But Moncrief also made a mistake after hitting a leadoff double. He was thrown out when Nick Hundley hit a comebacker and A’s right-hander Paul Blackburn whirled toward second base.

Then Kyle Crick left two on and two out for Hunter Strickland, who allowed both runners to score as the A’s stretched their lead.

Blackburn was starting in place of Sonny Gray, whom the A’s dealt to the New York Yankees in the run-up to the 1 p.m. non-waiver trade deadline.

The Giants did nothing at the deadline – their only move came a week earlier when they dealt third baseman Eduardo Nuñez to the Boston Red Sox for two prospects – but they were not wired to make any blow-up-the-roster trades.

The Giants might not be done dealing. Johnny Cueto would have been one of their better trade chips if not for his ongoing blister issues, and his contract – he’s owed $84 million over the next four years – makes it likely he could get through waivers and be traded in August.

It’s becoming increasingly clear that if the Giants can trade Cueto, they will – both to add an infusion of talent and also to free up their future payroll obligations. (No team has more money committed for 2019.)

First, Cueto has to get healthy. He was expected to throw 70 pitches in a rehab start Monday for Single-A San Jose. He threw just 34 in three innings, with no reason immediately disclosed.