A couple of new rules figured prominently as the New York Mets and the Oakland A's both won their season-opening games after months of baseball uncertainty during the coronavirus shutdown. Yoenis Cespedes took advantage of a new designated hitter rule to blast his first home run in his long-awaited return and lift the Mets to a 1-0 opening day win over the Atlanta Braves. Matt Olson smacked a walk-off grand slam homer in extra innings as Oakland became the first team to win a game under the new speed-up, extra-innings rules by beating the Los Angeles Angels 7-3 in the late game. Cespedes' solo shot in the seventh inning off reliever Chris Martin was his first homer since his last game in the majors on July 20, 2018. "Being able to hit a home run after being out for two years, it proved to me that I can still be the same player that I used to be," he said. Cespedes, who was sidelined with a broken right ankle and two heel surgeries, smacked the first-ever home run and RBI by a designated hitter in a National League stadium. "I don't care if he took a five-year hiatus, when he gets in the batter's box, you're worried," Braves manager Brian Snitker said. "He's such a presence." Friday's Mets opener kicked off the first full slate of games in the much-anticipated return to baseball after the global pandemic at times threatened to scuttle the entire season. The MLB season officially started Thursday with the New York Yankees rain-shortened 4-1 win over the Washington Nationals. After bitter wrangling between team owners and players, an abbreviated 60-game season was mandated by MLB commissioner Rob Manfred. Games are taking place without fans, while players are subject to a range of strict health and safety protocols designed to prevent outbreaks of COVID-19. In Chicago's Wrigley Field, the players from the Cubs and the Milwaukee Brewers took part in a pre-game ceremony, standing during the American anthem and holding up a black fabric in honour of Black Lives Matter. - America's pastime - The United States has been wracked by nationwide protests against racism and police brutality after the May 25 death of African-American George Floyd in Minneapolis at the hands of police officers. And because of the pandemic raging across American cities and towns at the same time, Friday's contests took place in eerily empty ballparks. Some of the players wore protective masks on the field and Seattle Mariners' Mallex Smith even batted with his face mask on. It is a striking contrast to the celebratory atmosphere that normally accompanies the opening day festivities of a sport regarded as America's pastime. In Chicago, hardcore fans milled around Wrigley Field or paid a premium to watch from the rooftop balconies of the buildings across the street. Fake crowd noise was piped in throughout the stadium and several venues filled the empty seats with hundreds of cardboard cutouts with pictures of fans adding to the faux atmosphere. "Opening day usually is winter coats and throngs of people," Cubs fan Kim Horvas said. "This is weird." Among the changes to American baseball this year is the addition of the designated hitter to the National League for the first time, and a runner being placed on second base to begin the 10th inning of games that go into extra innings. Both came into play on Friday night. MLB instituted the controversial extra-inning runner rule for this season to keep games from dragging on amid a compressed, 60-game schedule. In Oakland, the A's Marcus Semien began the bottom of the 10th on second base with the score tied 3-3. Semien moved to third while Ramon Laureano, who was hit by a pitch, reached second, and Khris Davis, who had walked, was at first when the Angeles brought in left-handed pitcher Hoby Milner and he delivered the game-ending pitch to Olson. Olson connected for a walk-off grand slam and the A's celebrated at home plate. Also, Shane Bieber struck out 14 over six scoreless innings in a historic outing as the Cleveland Indians beat the Kansas City Royals 2-0. The 25-year-old Bieber passed Bob Gibson and Lon Warneke for most strikeouts without allowing a run on Opening Day in MLB history. Cleveland wore their road jerseys with 'Cleveland' printed on the front as opposed to their home jersey with 'Indians' on it. The Indians announced previously they are considering a name change which would mean dropping the name they have used since 1915. New York Mets Yoenis Cespedes, 52, celebrates a 1-0 win with his teammates against the Atlanta Braves in after their opening day game at Citi Field A couple looks out over an empty stadium as the Los Angeles Dodgers play the San Francisco Giants in Los Angeles.