LOS ANGELES -- Bryce Harper's historically rapid return from Tommy John surgery brought with it questions surrounding timing, particularly his ability to catch up to major league pitching after spending so much of these past five months focused mostly on rehabilitation.

A different type of timing presented an obstacle.

Harper used his designated timeout during a two-strike count in his first at-bat against the Los Angeles Dodgers then again on a two-strike count in his second at-bat then again before even seeing the first pitch in his third. Harper, famously deliberate with his routine between and before pitches, wasn't merely playing in his first game of the season on Tuesday night. He was playing in his first game with a pitch clock, one of several new regulations introduced for the 2023 season. It's going to take some getting used to.

"Your whole life, your whole career, you've always slowed the game down," Harper said after the Philadelphia Phillies' 13-1 loss from Dodger Stadium. "I took a long time from the on-deck circle to the batter's box. And also in between pitches, I'd take a while. So, definitely an adjustment period. I just got to figure that out -- figure out what I want to do, how I want to do it, use my timeouts when I need to and understand the game's going to be at a quicker pace for the foreseeable future."

Harper, who batted third while serving as the designated hitter, went 0-for-4 with three strikeouts in what amounted to the second straight night in which the Dodgers scored 13 runs against the Phillies' pitchers.

It was an unceremonious return but also a particularly challenging one.

Harper's first assignment came in a left-on-left matchup against Julio Urias, who boasted the lowest ERA in the National League last season. Urias attacked Harper largely with breaking balls that tailed away from him, most of which Harper either fouled off or swung through. Harper whiffed on a 1-2 curveball low and outside in his first at-bat then grounded out on a check-swing tapper in his second and swung through a 1-2 cutter well outside in his third. His fourth at-bat, to lead off the ninth inning of a 12-run deficit against right-hander Phil Bickford, saw him take three swings, the last of which was a foul tip on an inside-corner cutter.

Phillies manager Rob Thomson believes Harper's bat speed was sound and that he was "on a lot of pitches," even if results didn't materialize.

"I was excited -- excited to get back, excited to be back," Harper said. "But not the game we wanted to have, right? Just got to keep going, keep plugging along. I feel like it's pitch selection. And it'll even things out; it'll get better. Just got to give it some time."

It's an understandable assessment. It was only 160 days ago, on Nov. 23, that Harper underwent surgery to repair a torn ulnar collateral ligament in his right elbow. The initial prognosis had him returning after the All-Star break, but Harper set his sights on this series -- from Dodger Stadium, the place where he made his major league debut 11 years ago -- as his target. It fueled him throughout the course of his rehab, gave him something to chase. He beat the initial timeline by more than two months and wound up returning from Tommy John surgery faster than any baseball player on record, according to research by ESPN Stats & Information.

"Obviously, he's not throwing a baseball, but he's swinging a baseball bat at full speed," Phillies hitting coach Kevin Long said. "It's a remarkable feat, and I guess it's another chapter in Bryce Harper's life."

The process began in early March, with two sets of 10 dry swings with a much lighter fungo bat from the Phillies' spring training complex in Clearwater, Florida. Over the course of roughly six weeks, Harper and Long progressed through tee work, soft toss, traditional batting practice, swings off a high-velocity pitching machine and live at-bats. Harper received the equivalent of 50 at-bats against either rehabbing pitchers or minor league pitchers over these past handful of weeks, opting for controlled environments instead of venturing out on a traditional rehab assignment.

Harper received final clearance from Dr. Neal ElAttrache, who performed his surgery, in L.A. on Monday. Thomson had decided to give Harper that night off regardless and was hesitant to start him with such a tough matchup in Urias, a perennial Cy Young contender, the following day. But Harper, he said, wanted it.

"He wants to play," Thomson added. "He's itching to play."

Harper was noticeably aggressive in his return, swinging at the first pitch each of the four times he came to bat. He will return to the lineup for Wednesday's series finale, a day game, and is expected to play regularly given that the Phillies begin this month with four days off in a stretch of three weeks. Eventually, once his throwing progression reaches a certain point, he'll transition to first base. But that development is still months away. For now, the Phillies simply need his bat in the lineup.

"I want the results to be better," Harper said of his first game back. "But granted, I'm excited to be back. Going through six months of grinding, hard work, and to be able to get back today, I was extremely excited."

Harper spent the vast majority of the 2022 season nursing a tear in his right UCL and serving as the Phillies' DH, batting .296/.368/.522 in 90 games there during the regular season then hitting four go-ahead home runs in an epic postseason run that culminated in a World Series appearance. That year, though, Harper ranked 11th among 376 hitters in slowest tempo between pitches with the bases empty, as measured by Baseball Savant. In other words, he took a long time in the batter's box.

Now, in a new wrinkle, he'll have a pitch clock to work against.

"It's going to be an adjustment for me," Harper said. "But it is what it is at this point."